Super Simple Physics - The Ultimate Bitesize Study Guide

Atoms and radioactivity 251

Chain reactions
A nuclear chain reaction is a series of fission
reactions, each caused by neutrons released
in a previous fission reaction. Uncontrolled
chain reactions, such as in a nuclear weapon,
can cause the explosive release of a vast
amount of energy.

A neutron collides with
a uranium-235 nucleus,
splitting it and causing the
release of a burst of energy.

Neutrons released by the
fission collide with more

uranium-235 nuclei.

Each time the Initial neutron Uranium nucleus
process causes
a larger number Absorbed by
of nuclei to split. control rods

Controlled chain reactions

Nuclear chain reactions can build, fade, or remain stable
depending on how many fission reactions are caused by
the products of a previous fission. If each fission reaction
leads on average to only one more, this results in a stable
(controlled) chain reaction. Nuclear power stations control
chain reactions by inserting control rods into the reactor
core. These absorb neutrons, slowing the reaction down.

252 Atoms and radioactivity Key facts

Nuclear power ✓ Nuclear power plants use

Nuclear power is the generation of electricity using nuclear the energy from nuclear
fission as a source of energy. Nuclear power plants generate fission to generate heat
about 10 percent of the world’s electrical power. Making use and electricity.
of nuclear energy means that we use less fossil fuel.
✓ Nuclear power does
Nuclear reactor
A nuclear reactor contains radioactive uranium in fuel rods. Placing not generate carbon
these close together triggers a chain reaction that releases large dioxide emissions.
amounts of energy. The energy released boils water to make steam,
which powers generators. The reaction is managed by moving ✓ Nuclear power stations
control rods in and out of the reactor core. These absorb neutrons
and slow the chain reaction down. create hazardous
radioactive waste that must
Control rods are raised or lowered into be disposed of carefully.
the core to stop neutrons from
traveling between fuel rods, changing Steam
the speed of the chain reaction.

A gas called a The coolant The steam drives
coolant is heated transfers energy turbines, which turn
to water to electricity generators.
by the nuclear create steam.
reaction.
Water pump Cooled water
Pressure
vessel

Uranium
fuel rods

Radioactive waste

Graphite Unlike fossil fuel power stations, nuclear power stations
moderators slow don’t emit carbon dioxide. However, the used nuclear fuel
stays radioactive for thousands of years and must be safely
down neutrons stored in disposal facilities until it no longer poses a threat.
released by The most dangerous and long-lasting
wastes are buried very deep
nuclear fission to underground. Less hazardous
make them more and shorter-lived radioactive
waste is sealed in concrete
effective in the casks and buried in
chain reaction. shallow pits.

Coolant pump

The most hazardous waste is
buried deep underground.

Atoms and radioactivity 253

Fusion Key facts

Nuclear fusion—in which two or more atomic ✓ Nuclear fusion occurs when atomic
nuclei fuse to form a heavier nucleus—is the process
nuclei are forced together to form a

that powers the Sun. Scientists and engineers are heavier nucleus.

working on ways of harnessing this source of energy ✓ During nuclear fusion, a small amount

to generate electricity. of mass is converted into energy.

✓ Extreme heat and pressure are

Hydrogen fusion required to initiate fusion.
During nuclear fusion, the nuclei of two atoms are forced
together by very high temperatures and pressures. The reaction 3. Helium is
here shows the hydrogen isotopes deuterium (hydrogen-2) and
tritium (hydrogen-3) fusing to create a helium nucleus. The new a product of
helium nucleus and the ejected neutron have slightly less mass the reaction.
than the two hydrogen nuclei. The lost mass is converted
to energy.

2. The nuclei Helium-4
(stable)
fuse to form a
larger nucleus.

1. Two hydrogen Hydrogen-2 4. A tiny amount of

nuclei collide. mass is converted
to a lot of energy.

Helium-5
(unstable)

Hydrogen-3 Neutron

Harnessing fusion In the core of this
fusion reactor, hot
The nuclei of atoms are positively charged and repel matter is confined
each other, so fusion can only take place if nuclei
are pushed extremely close together, overcoming this by magnetic
repulsion. This is why fusion only occurs in extremely fields in a donut-
hot and high-pressure environments like the cores of
stars. These requirements make it very difficult to build shaped ring.
a fusion reactor on Earth to initiate and sustain fusion.
Scientists working at experimental fusion reactors have
briefly sustained fusion using powerful magnetic fields to
confine the hot matter. However, it currently takes more
energy to run the reactor than the reactor produces.

Space

Space 255

Structure of Earth Key facts

Studies of seismic waves from earthquakes (see page ✓ Earth’s interior has four distinct
123) reveal that Earth’s interior consists of distinct layers.
Heavier elements, such as metals, are concentrated in layers: the inner core, outer core,
the planet’s center, while lighter materials, such as rock, mantle, and crust.
form the outer layers.
✓ The crust and uppermost part of the
Inside Earth
Earth’s interior consists of four distinct layers: the inner core, mantle form a rigid structure that is
outer core, mantle, and crust. The crust and the uppermost divided into tectonic plates, which
part of the mantle are joined to form a rigid structure called move slowly over time.
the lithosphere, which is divided into sections called tectonic
plates. These move very slowly over time, changing the shapes ✓ The atmosphere is a layer of gases
of continents and oceans.
trapped by gravity.
The inner core is a ball The outer core consists
of iron and nickel, which mainly of molten iron. The atmosphere
is very hot but solid due Currents in this fluid
generate Earth’s Earth’s atmosphere is a mixture of gases
to high pressure. magnetic field. that are held in place by gravity. The
atmosphere is divided into layers with
distinct properties. It has no clear upper
edge and fades gradually into space.

Exosphere
This is the outermost layer and by
far the tallest. Gas molecules can

escape into space from here.

Thermosphere
The International
Space Station orbits
Earth in this layer.

Mesosphere
This is where meteors
(shooting stars) burn up.

The crust is a thin outer The mantle is a layer of rock Stratosphere
layer of solid rock. The crust that makes up about two-thirds Ozone gas in this
of Earth’s mass. It is mostly layer absorbs harmful
and the top part of the solid but can flow over very UV light from the
mantle form the lithosphere. long periods of time. Sun. Airliners fly in
the lower stratosphere.

Troposphere
All weather occurs

in this layer.

256 Space Spring in the northern
hemisphere, fall in
Seasons the southern hemisphere

It takes 365 days—which we call a year—for Earth to
complete one orbit around the Sun. The cycle of seasons
happens because Earth’s axis of rotation is tilted. As a
result, parts of the planet that tilt toward the Sun get more
sunlight each day than parts tilted away from it.

Earth’s axis
of rotation is
tilted 23.5°.

When the North Pole is
tilted toward the Sun, it
is summer in the northern
hemisphere and winter in
the southern hemisphere.

Changing sunlight
Earth’s axis of rotation remains at the same angle all year round.
The hemisphere that is tilted toward the Sun experiences
longer days and stronger heating from the Sun, while the
one that is tilted away has shorter days and is heated less.

The Sun’s path

During summer, the Sun is visible for longer each (top) and midwinter (bottom). Between them is
day and reaches higher in the sky than in winter. This its path through the sky during the spring and
time-lapse photo from a northern-hemisphere location fall equinoxes—the two times of year when
shows the Sun’s path through the sky in midsummer day and night are the same length.

East Summer West

Spring/Fall

Winter

Fall in the northern Space 257
hemisphere, spring in the
southern hemisphere Key facts

The regular change from ✓ The cycle of seasons
night to day is caused by
Earth’s rotation. happens because Earth’s
axis is tilted.

✓ When the North Pole is

tilted toward the Sun,
it is summer in the
northern hemisphere.

✓ When the South Pole is

tilted toward the Sun,
it is summer in the
southern hemisphere.

When the South Pole is
tilted toward the Sun, it
is summer in the southern
hemisphere and winter in
the northern hemisphere.

Solar heating The North Pole is tilted The Sun’s rays are spread
toward the Sun during over a wider area, so the
Because Earth is spherical, the northern summer. Sun does not feel as hot.
sunlight hits the planet’s
surface at an angle in the Sunlight is more
north and south, spreading concentrated when it
the Sun’s energy over a spreads over a smaller area.
much larger area. As a result,
the Sun feels much cooler
at midday in winter than
in summer, and tropical
countries are usually much
warmer than countries
farther from the equator.

The South Pole
is tilted away from
the Sun during the

southern winter.

258 Space Jupiter, Saturn, Uranus, and Neptune
are giant gaseous planets that orbit
Solar system the Sun beyond the asteroid belt.

The solar system is the region of space influenced Uranus
by the Sun’s gravity. It has eight major planets
(including Earth); the moons that orbit them; and
countless smaller objects, such as dwarf planets,
asteroids, and comets. All of these objects are held
in orbit around the Sun by its gravity.

Mercury, Venus, Earth, and
Mars are rocky planets
and orbit near the Sun.

Jupiter

The Sun is
our local star.

Earth
Mars

Mercury

Venus
Asteroids—small, rocky

bodies—are mostly confined
to a broad circular belt

between Mars and Jupiter.

Beyond Neptune’s orbit is the Space 259
Kuiper belt—a vast disk of small,
icy bodies, including dwarf planets. Key facts

Neptune ✓ Objects in the solar system are held in orbit by

the Sun’s gravity.

✓ Planets are large, spherical objects that orbit a

star and that clear their orbits of other material.
There are eight in the solar system.

✓ Moons (natural satellites) are large bodies that

orbit planets.

✓ Asteroids are small, rocky bodies that are mostly

found between Mars and Jupiter.

Smaller bodies

Saturn Pluto Dwarf planets
Objects with enough mass to
form a spherical shape but not
enough to clear their orbits of
other material are called dwarf
planets. Pluto is the best-known
dwarf planet.

Comets
Comets are made from a mix
of rock and ice. They have
long, elliptical orbits and often
develop bright tails as they
travel close to the Sun.

Comet Lovejoy

The planets Asteroid Ida Asteroids
Planets are large, spherical Enceladus Asteroids are usually irregular
objects that orbit a star and that bodies made of rock and metal
have sufficient mass to clear their left over from the formation of
orbits of other material. The solar the planets. Most asteroids
system’s four innermost planets orbit the Sun between the
are rocky planets—solid balls of orbits of Mars and Jupiter.
rock and metal. The planets of
the outer solar system are much Moons
larger and more widely separated. Moons are large bodies that
They all have thick atmospheres orbit planets and are sometimes
of gases, including hydrogen and called natural satellites. There
helium, and each has a system of are more than 200 moons in the
rings and moons orbiting it. solar system, most of which orbit
the giant planets.

260 Space Key facts

The Moon ✓ The Moon is a natural satellite

The Moon is a natural satellite of Earth and orbits of Earth.
our planet once every 27.3 days. It doesn’t produce
its own light, but we can still see it because it reflects ✓ The Moon passes through a series
light from the Sun.
of phases every 29.5 days.
Lunar phases
Every 29.5 days, the Moon passes through a series of phases ✓ Tides are primarily caused by
as we see different parts of its surface illuminated by the Sun.
When the Moon is directly between Earth and the Sun, it the pull of the Moon’s gravity on
cannot be seen from Earth and is called a new moon. When Earth’s oceans.
it’s on the opposite side of Earth from the Sun, we see its
whole face illuminated: a full moon. We always see the same 7
face of the Moon because tidal forces exerted on the Moon 86
by Earth slowed the Moon’s period of rotation over millions
of years until it matched the time it takes to orbit Earth once. 15

24
3

1. New moon 2. Waxing crescent 3. First quarter 4. Waxing gibbous

5. Full moon 6. Waning gibbous 7. Last quarter 8. Waning crescent
Tidal bulge
Tides
Gravity
Ocean tides are caused mainly by the Moon’s gravity. The High tide
Moon’s gravity is strongest on the side of Earth facing the Moon,
as it is slightly closer. This force pulls the ocean toward the
Moon, causing a slight bulge. On the opposite side of Earth,
where the Moon’s gravity is weakest, inertia causes the water to
bulge in the opposite direction as it tries to keep moving in a
straight line. As a result, high tides occur twice a day.

Eclipses Space 261

Eclipses happen when Earth, the Sun, and the Moon Key facts
line up in space. When the Moon passes directly
between the Sun and Earth, it casts a shadow on ✓ Eclipses occur when Earth, the Moon,
Earth and creates a solar eclipse. A lunar eclipse
happens when Earth casts its shadow on the Moon. and the Sun line up.

✓ Solar eclipses happen when the Moon

casts a shadow on Earth.

✓ Lunar eclipses happen when Earth

casts a shadow on the Moon.

Solar eclipse A total solar eclipse
Solar eclipses happen when the occurs where the Sun
Moon comes directly between is completely blocked
the Sun and Earth and so casts by the Moon.
a shadow on part of Earth’s
surface. Although the Moon A partial eclipse occurs
is much smaller than the Sun, where the Sun is only partly
it is much closer to Earth and
can block the Sun completely, blocked by the Moon.
causing a total solar eclipse.
When they occur, total solar
eclipses are visible from only
a small part of Earth.

Lunar eclipse The Moon passes through the
Lunar eclipses occur during a full shadow cast by Earth.
moon if the Moon passes through
Earth’s shadow. Sometimes only The Moon’s surface is darkened,
part of the Moon passes through but some light shines onto it
Earth’s shadow, but when the through Earth’s atmosphere.
whole Moon falls in Earth’s shadow,
the Moon can turn a reddish color.
This is because light refracted
(bent) through Earth’s atmosphere
can still reach the Moon’s surface.

The Sun’s atmosphere

When the Moon completely obscures the
Sun during a total solar eclipse, astronomers
can see the Sun’s faint outer atmosphere—
the corona. The corona extends millions
of miles (kilometers) into space but is
difficult to study because it is usually hidden
by the Sun’s glare.

262 Space Key facts

Orbits ✓ An orbit is the path that an object

The planets of the solar system travel around the takes as it moves around another
Sun because they are trapped by the force of gravity. object in space.
The paths that planets follow around the Sun or that
moons follow around planets are called orbits. ✓ The force of gravity causes objects

Shapes of orbits in space to travel in orbits.
The planets in the solar system have nearly circular orbits. The
pull of gravity from the Sun provides the centripetal force (see ✓ Orbits can be circular or elliptical.
page 96) that stops them from flying away in a straight line. ✓ In a circular orbit, an object’s speed
Smaller bodies, such as comets, have very elliptical orbits. Their
speed increases as they get closer to the Sun. is constant but its velocity is always
changing as its direction is changing.
An ellipse is an oval
shape that is longer on In a circular orbit,
one axis than the other. an object’s speed is
constant but its velocity
Comet is continually changing
due to the changing
direction of motion.

The comet would The Sun is at Direction
continue to move in the focal point of motion
this direction if the
Sun’s gravity were of the orbits. Earth
not acting on it.
Earth’s orbit is not a
perfect circle but is close.

Types of orbit

Artificial satellites are placed in different types of orbit depending on the job
they do. Two common types of satellite orbit are geostationary and polar.

Equator

Geostationary orbits Polar orbits
Geostationary satellites stay above the Satellites with polar orbits travel
equator and complete one orbit every around the planet from pole to pole.
23 hours 56 minutes, matching Earth’s Because Earth rotates beneath them
period of rotation. This means they stay while they orbit, they pass over
above the same point on the planet all different parts of the planet with
the time. Geostationary orbits are used for each orbit. Polar orbits are used for
weather and communications satellites. Earth-monitoring satellites.

Space 263

Galaxies Key facts

A galaxy is a spinning group of stars held together by gravity. ✓ Galaxies are groups of stars
The Universe may have as many as 2 trillion galaxies, and
each galaxy may hold billions or trillions of stars. Vast held together by gravity.
distances separate galaxies and the stars within galaxies.
✓ The different types of
Types of galaxy
Galaxies can be sorted into different kinds based on their shape. galaxy include spiral,
These include spiral, barred spiral, lenticular, elliptical, and irregular. barred spiral, lenticular,
The Sun is part of the Milky Way galaxy, which is a barred spiral elliptical, and irregular.
galaxy—a spiral galaxy with a central bar shape made of stars. All the
stars we see in the night sky belong to the Milky Way. The artist’s ✓ Our solar system is in the
impression below shows what it might look like from outside.
Milky Way galaxy.
Spiral arms At the center of the
extend from the Milky Way is a black hole Scale of
galaxy’s center. called Sagittarius A*. the Universe

Stars are Distances in space are so great
more densely that we measure them in light-
packed in the years. One light-year is the
center of a distance light travels in a
spiral galaxy. year: about 9.5 trillion km.

The Sun is 8
light-minutes
from Earth.

The Milky Way is Our solar system Our nearest
about 2 million is located in the neighboring
Orion arm. star, Proxima
light-years across. Centauri, is 4.2
light-years away.

Polaris, the North
Star, is 320 light-
years away.

Lenticular galaxies, like Elliptical galaxies are Irregular galaxies have We are 26 000
spiral galaxies, are shaped like a squashed no particular shape light-years away
disk-shaped with a sphere. The stars in and lack spiral arms. from the center
central bulge. However, elliptical galaxies tend About a quarter of all of the Milky
they lack spiral arms. to be older than those galaxies are irregular. Way galaxy.
in other galaxy types.
Andromeda, the
galaxy closest to
us, is 2.5 million
light-years away.

264 Space

Observing space Key facts

The main way we learn about the Universe is by capturing the ✓ Astronomers use different
visible light and other radiation that reaches Earth from far away.
Telescopes are tools that collect this radiation and produce images kinds of telescopes to pick
that are brighter and more detailed than the naked eye can see. up different kinds of
electromagnetic radiation
Telescopes from objects in space.
Our understanding of space has been transformed over the past century
thanks to powerful telescopes. Early astronomers had to draw what they ✓ Some telescopes are
saw, but today cameras record images and computers are used to analyze
them. Astronomers use telescopes located both on Earth and in space to sent into space to give
capture and study radiation from the whole electromagnetic spectrum. us clearer images.

Arecibo’s primary dish The curved shape of the dish A set of mirrors This image of the
is 305 m wide. focuses radio waves. inside reflects light Pillars of Creation in
the Eagle Nebula
onto a detector. was formed from
digital images
taken by the HST.

Light enters
here.

Solar panels provide
electricity to operate

the telescope.

Telescopes on Earth Space telescopes
Earth-based telescopes, such as the Arecibo Observatory in Puerto Like most modern telescopes, the Hubble Space Telescope (HST)
Rico, can be much bigger than space telescopes because they don’t uses mirrors rather than lenses to collect and focus light. Orbiting
need to be launched into space. Radio telescopes such as Arecibo telescopes such as Hubble can observe space without clouds and
need huge dishes because radio waves have a much longer dust in the atmosphere getting in the way and can detect types of
wavelength than visible light. radiation absorbed by Earth’s atmosphere, such as infrared.

Invisible radiation at different frequencies. These pictures show the
Crab Nebula—the glowing remains of a star that
Stars and other space objects give off radiation across exploded—in different electromagnetic frequencies.
the whole electromagnetic spectrum. Astronomers can
learn more about objects in space by studying images

Radio Infrared Visible light Ultraviolet rays X-rays

Space 265

Redshift Key facts

When astronomers analyze the light from distant galaxies, ✓ Redshift is an increase in the
they find that its wavelength is slightly longer than that of
light from closer objects. This difference, imperceptible to wavelength of light from distant
the naked eye, is caused by an effect called redshift, and galaxies that are receding (moving
it shows that the Universe is expanding. away from us).

Moving light ✓ Redshift studies show that the
Light waves from objects that are receding (moving away) have a
slightly elongated wavelength. The faster the object is receding, farthest galaxies are receding fastest.
the greater the increase in wavelength. By studying redshift,
astronomers discovered that the farthest galaxies are receding ✓ The observed redshift provides
fastest. This shows that the whole Universe is expanding in a
pattern that supports the Big Bang theory (see page 267). evidence that the Universe is
expanding and supports the
Big Bang theory.

Moving away Light waves from receding galaxies
are stretched, resulting in longer
wavelengths (redshift). Redshift
is seen in nearly all galaxies.

Moving toward Light waves from galaxies moving
toward us are compressed, resulting
in shorter wavelengths (blueshift).
Blueshift is seen in very few galaxies.

Studying starlight Receding galaxy (redshifted)
Laboratory spectrum (stationary)
Astronomers study the light from stars and galaxies with a technique Approaching galaxy (blueshifted)
called spectroscopy. In one form of spectroscopy, the visible light from a
star has distinctive black gaps because chemical elements in stars or in
space absorb and block certain wavelengths. Redshift (or occasionally
blueshift) causes these lines to shift, and the amount they move reveals
how fast a star or galaxy is moving toward or away from us. Redshift
affects all kinds of electromagnetic radiation, not just visible light.

266 Space Beginning of the known Universe

Expanding The first galaxies formed
Universe around 600 million
years after the Big Bang.
The light from stars and galaxies can
be analyzed to find out whether they Expanding space
are moving toward us or away from Hubble’s discovery revealed that the
us. In 1929, astronomers, including
Edwin Hubble in the US, discovered Universe is expanding. Astronomers
that most galaxies are moving believe that galaxies are speeding away
away from us at a speed that is
proportional to their distance. from us not because they are traveling
We call this Hubble’s law. through space, but because space
itself is expanding. Measurements
Gravity keeps clusters of the rate of expansion indicate
of galaxies together. that the observable Universe
began around 13.8 billion
years ago in an event called
the Big Bang.

The space
between galaxies
is expanding.

The Universe Dark matter and dark energy
expands over time.
Measurements of the light from Normal matter makes Dark energy drives
Key facts
supernovas in distant galaxies up the stars and parts the expansion of
✓ Most galaxies are
suggest that the expansion of the of galaxies we can see. the Universe.
moving away from us.
Universe is accelerating. Scientists 5%
✓ The speed at which
think the acceleration is driven
galaxies are moving
away increases in by an unknown source of energy, Dark matter
proportion to their
distance from us. named dark energy. They also holds galaxies

✓ Hubble’s observations think there must be more mass together and is 27 %
in galaxies than we can see, as thought to be
show the Universe is there isn’t enough visible mass everywhere in 68 %
expanding and support to properly explain the observed the Universe.
the Big Bang theory.
motion of stars and galaxies.

The undetected mass is called

dark matter.

Content of the Universe

Big Bang or Space 267

steady state? Key facts

There are two different theories to explain the ✓ The Big Bang theory says the Universe
expansion of the Universe. The Big Bang theory says
that the expansion can be traced back to a beginning began at a single point 13.8 billion
at a single point. The steady-state model says that years ago and has been expanding
something is continuously creating matter and ever since.
making the Universe expand.
✓ The steady-state model says that

matter is continuously created to fill
the Universe as it grows.

✓ The Big Bang is the currently

accepted theory and the steady-state
model is now considered incorrect.

The Big Bang theory
According to the Big Bang theory, space expanded suddenly
from a single point of origin 13.8 billion years ago. All the
matter and energy the Universe would ever have was present
from the beginning. As the Universe expanded, matter and
energy became ever more widely spread. Most evidence
suggests the Big Bang theory is correct.

Matter formed as the The galaxies get
Universe expanded farther apart as
and cooled. space expands.

Steady-state model New matter is created as
According to this rival model, proposed in the early the Universe expands,
20th century, the Universe has always existed and so the density stays the
is continually expanding as new matter is created. same everywhere.
However, scientific observations don’t support the
model, and it is now considered incorrect.

Cosmic microwave background radiation Cosmic microwave
background radiation
In 1964, two radio astronomers discovered a weak radio signal
coming from all over the sky. They realized they had picked up
radiation from the Big Bang that is now spread thinly across the
entire Universe. The existence of this energy had been predicted
by the Big Bang theory but not the steady-state model, so its
discovery supported the Big Bang.

268 Space Key facts

Star life cycles ✓ Stars form from clouds of gas and

Stars form inside gigantic clouds of gas and dust dust called nebulas.
that contract due to the force of gravity until
nuclear fusion reactions are triggered inside them. ✓ Planets form from the debris left
The life cycle a star passes through as it ages and
uses up its fuel depends on the star’s mass. behind after star formation.

Different lives ✓ The stages in a star’s life depend
The diagram here shows the typical life cycles of
massive stars (along the top) and stars the size of our on its mass.
Sun (bottom). Massive stars shine brilliantly, use their
fuel quickly, and die in a spectacular explosion. Smaller When a massive star runs
stars use their fuel slowly and shine for longer before out of fuel, it swells to
swelling as they age and then fading away. form a supergiant.

All stars form in Massive
nebulas—giant clouds star
of gas and dust.

A pocket of gas contracts to As an average-sized star
form a dense, spinning runs out of fuel, it swells

clump, eventually triggering to form a red giant.
nuclear fusion in the core.
Average-sized
star

Stellar equilibrium Normal star Red giant Black hole
In a star like our In an aging star, the core When the most massive
Stars shine stably as long as they Sun, the inward pull heats up and the forces stars run out of fuel, the
can maintain a balance between of gravity balances become unbalanced. The force of gravity far exceeds
the inward pull of their own gravity outward pressure star swells in size until pressure from the core
and the outward pressure of from the core. the forces balance again. and the star collapses
radiation from fusion reactions It is now a giant star. into a black hole.
in the core. When the fuel inside
the star begins to run out, the
forces become unbalanced and
the star changes, sometimes
dramatically and violently.

Star formation Space 269

Stars form in vast, interstellar clouds of gas and dust called nebulas. The remains of the core may
If a nebula is disturbed—for instance, by a shock from an exploding contract to form an incredibly dense,
star—part of it may start to contract due to gravity to form a dense, fast-spinning star the size of a city. All
rotating clump. As the clump becomes more dense, its gravitational matter is crushed to form neutrons,
pull grows stronger, drawing more material in, and its core heats up. so such stars are called neutron stars.
Eventually, the core is so dense and hot that nuclear fusion reactions
are triggered, causing a star to shine. The remaining material orbits the
star as a disk of dust and gas in which planets and other bodies form.

When a supergiant runs out of fuel,
it collapses suddenly and

then explodes. We call this
explosion a supernova.

When nuclear fuel in the core of Cores of the most massive stars
an average star is used up, the star collapse to form a black hole—a
sheds its outer layers of gas into space
and the core collapses into a hot, region in which gravity is so
Earth-sized star called a white dwarf. strong that not even light can

escape its pull.
Eventually, the star may cool to

form a ball of carbon that emits

no light or heat—a black dwarf.

These take so long to form that

none are thought to exist yet.

Making elements Hydrogen fused
Helium fused
Stars are made mostly of hydrogen, the simplest element Carbon fused
in the Universe. They shine by nuclear fusion (see page Neon fused
253): hydrogen nuclei are forced together to form larger Oxygen fused
atomic nuclei, such as helium, releasing energy in the Silicon fused
process. Toward the end of a star’s life, its core runs out Iron core
of hydrogen and starts to fuse other elements instead.
Sunlike stars fuse helium to make carbon, and more Core A supergiant star
massive stars go on to make heavier elements such as
nitrogen, oxygen, and iron. When massive stars explode
as supernovas, elements even heavier than iron are
produced, and the explosion scatters the elements
through space to form new nebulas. Many of the
chemical elements in our bodies formed this way.

270 Space

Classifying Key facts

stars ✓ The light from a star can be used to calculate its temperature.
✓ Apparent magnitude is how bright a star appears from Earth.
Stars may look like pinpricks of light to ✓ Absolute magnitude is how bright a star appears from a
the naked eye, but astronomers can
use the light they emit to calculate standard distance.
their temperature, distance from
Earth, diameter, and mass. These ✓ A Hertzsprung–Russell diagram is a graph showing the
characteristics are used to classify
stars and work out their age and temperatures of stars plotted against brightness.
how long they have left to live.

Red
supergiant

Red Blue
giant hypergiant
Orange
giant Blue
supergiant
White Red The
dwarf dwarf Sun Star size
Stars vary enormously in size, from neutron stars no
bigger than a city (but with more mass than our Sun) to
supergiants and hypergiants millions or billions of times
greater in volume than the Sun. The characteristics of a
star depend mainly on its mass. The more massive a star is,
the hotter, brighter, and bluer it will be for most of its life,
but the shorter its lifespan. This is because massive stars
burn through their nuclear fuel more quickly.

Space 271

Color and temperature Hertzsprung–Russell diagrams

All objects emit radiation, whatever their About 100 years ago, the Danish astronomer Ejnar Hertzsprung and
temperature. As the temperature of an the US astronomer Henry Russell independently discovered a pattern
object rises, the amount of radiation it in the properties of stars. If stars are plotted on a graph of brightness
emits increases, but the peak wavelength against temperature, they form a distinctive pattern that reflects their
of the radiation decreases. That’s why the stage of life. Most stars occupy a diagonal band called the main
light from a very hot object changes from sequence. These are stars that are relatively small in volume and
red-hot to white-hot as its temperature that fuse hydrogen in their cores. Other stars, such as aging
rises. Astronomers use this principle giant stars that are running out of fuel, form clusters away from
to measure the surface temperature of the main sequence.
stars. Although not always obvious to
the naked eye, cooler stars emit red light Blue supergiants Red supergiants
more strongly and hotter stars emit blue
light more strongly. Brighter

Hot, blue star Sunlike stars evolve
into red giants and
Sunlike yellow star then white dwarfs
Cool red star
as they age.
0 500 1000 1500 2000
Energy Giants
Wavelength (nm)
Fainter White Main-sequence stars Cooler
dwarfs

Hotter

Magnitude These two stars look
equally bright in the night
Astronomers use the word magnitude sky, but in reality, star A is
for the brightness of a star. There are two brighter but farther away.
ways of measuring magnitude. Apparent
magnitude is how bright a star looks from A
Earth, but this can be misleading, as distant B
stars look fainter. Absolute magnitude is
a standardized measure of how bright all
stars would look from the same distance
(32.6 light-years).

Earth

272

Glossary

Absolute magnitude The brightness of Ammeter A device that measures Average speed The average speed of
a star when observed from a standard electrical current. a journey is the total distance traveled
distance. This is useful for comparing divided by the time taken. See also
the brightness of stars regardless of their Ampere (A) The unit of electrical current, instantaneous speed.
distance from Earth. often called an amp.
Background radiation Low-intensity
Absolute zero The lowest temperature Amplitude The maximum displacement radiation that is around us all the time.
possible, when all atoms stop moving. In of a wave from its average position. It is the Some of it is emitted by radioactive
the three main temperature scales (Kelvin, height of a wave’s peak above the midline substances in rocks and other materials
Celsius, and Fahrenheit), absolute zero is (half the vertical distance from the peak of around us, and some comes from space
0 K, –273°C, and –459°F. a wave to a trough). (cosmic radiation).

Absorption spectrum A pattern of dark Angle of incidence The angle between Balanced forces The forces acting on an
lines in the spectrum of light that has the incident (incoming) light ray and the object are balanced if they add up to a net
passed through a gas, such as in the normal line. force of zero newtons. For example, the
outer layers of a star. These lines show forces on a cyclist are balanced when
the wavelengths of light absorbed by the Angle of reflection The angle between the the forward force from pedaling is equal to
gas, which represent elements present reflected light ray and the normal line. the forces of air resistance and friction.
in the star.
Apparent magnitude How bright a Battery Two or more electrical cells
Acceleration The rate of change of velocity. star appears to us on Earth. See also connected in series make up a battery.
Acceleration can mean speeding up, slowing absolute magnitude. See also cell.
down, or changing direction. Acceleration is
a vector quantity. Units are m/s2. Asteroid A rocky body that orbits the Sun. Becquerel (Bq) A unit of radioactive
Most asteroids are in the asteroid belt decay. 1 Bq means that, on average, one
Acceleration due to gravity The rate at between Mars and Jupiter. atomic nucleus is decaying each second in
which a falling object accelerates due to the sample being measured.
gravity in the absence of air resistance. Asteroid belt A region between the
On Earth, this is about 9.8 m/s2 and often orbits of Mars and Jupiter where many Beta decay A form of radioactive
rounded to 10 m/s2. asteroids exist. Jupiter’s strong gravity decay in which an atomic nucleus
prevents the asteroids from forming a gives off a beta particle.
Aerodynamic Relating to the way air new rocky planet.
moves over objects. It is often used to Beta particle A high-speed electron. Beta
mean a smooth shape that reduces Atmosphere The layer of air that particles are emitted from some atomic
air resistance. surrounds a planet. nuclei during radioactive decay.

Air resistance The force that resists the Atmospheric pressure The force of Big Bang The event in which the Universe is
movement of objects through the air. the atmosphere pressing on a square thought to have begun, around 13.8 billion
This force is mostly due to collisions meter of Earth’s surface, caused by years ago, rapidly expanding from a
with air particles. the weight of air above. Units are singularity (a single point).
Pascal (Pa), where 1 Pa = 1 N/m2.
Alpha decay A form of radioactive Biofuel Any fuel made from recently living
decay in which an atomic nucleus Atom The smallest part of an element plant or animal matter—for example, the
gives off an alpha particle. that has the chemical properties of that conversion of sugar cane into ethanol fuel.
element. An atom is made up of protons, If the sugar cane is regrown as quickly as
Alpha particle A particle that consists of neutrons, and electrons. it is harvested, then this biofuel can be
two neutrons and two protons (the same considered renewable.
as a helium nucleus). Alpha particles are Atomic energy Sometimes referred
emitted from some atomic nuclei during to as nuclear energy, this is energy Bond A force between atoms or molecules
radioactive decay. stored in the bonds between the that holds them together. Chemical reactions
neutrons and protons in an atomic involve the making and breaking of bonds.
Alternating current (a.c.) An electric nucleus. This energy may be released
current that reverses direction at regular during nuclear fission or nuclear fusion. Braking distance The distance traveled by
intervals. See also direct current (d.c.). a vehicle from the moment the brake is
Atomic number Sometimes called pressed until the vehicle stops.
Alternator An electric generator that the proton number, this is the
makes alternating current from mechanical number of protons in an atom’s Cell A device that stores energy and
motion, usually by spinning a coil of wire nucleus. Each element has a produces an electric current when it is
in a magnetic field. See also generator. different atomic number. part of a complete circuit.

273

Celsius A temperature scale based on the Closed system A system that matter does Contamination Contamination occurs
freezing point (0°C) and boiling point not leave or enter. However, energy may when unwanted, often toxic substances
(100°C) of water at sea level. enter or leave the system. See also system. enter a system, such as radioactive
material entering a human body. See
Center of mass Sometimes called the Comet A mass of ice and rock that travels also irradiation.
center of gravity, this is a point in an around the Sun in an elliptical orbit. Some of
object where all its weight appears to be the dust may stream out to form a tail that Continuous variable A variable that can
concentrated. You can balance a pencil points away from the Sun. take any value (between limits) and is
halfway along its length because that’s not limited to whole numbers, such as a
where its center of mass is. Compass A device containing a person’s height. See also discrete variable.
small magnetic needle allowed to
Centripetal force A pulling force rotate freely. The needle lines up Control variable A variable that needs
that causes an object to move along with Earth’s magnetic field. to be kept constant in an experiment.
a curved or circular path—for example, This is done to see properly the effect of
the tension force in a string tied to a Component of a force The part of a force changing the independent variable on the
heavy object that’s being swung around that acts in a particular direction. For dependent variable—for example, keeping
in circles. example, when pushing a wheelbarrow, room temperature constant during an
some of your push force moves the experiment to measure the temperature
Chain reaction A chemical or nuclear wheelbarrow forward (horizontal) of hot water as it cools.
reaction in which the products trigger and some acts upward, lifting the
similar reactions. Uncontrolled chain wheelbarrow (vertical). Convection The transfer of heat through a
reactions can cause explosions. fluid (liquid or gas) caused by particles rising
Compound A substance consisting of from hotter, less dense areas and sinking
Change of state A change between two two or more elements whose atoms from cooler, more dense areas.
states of matter (solid, liquid, gas). have bonded.
Converging lens A lens that curves
Charge (or electric charge) A basic property Compression Pressing together outward in the middle. Also called a
of some particles, such as electrons or or squeezing. convex lens. Converging lenses make
protons, that makes them feel a force in parallel beams of light come together.
an electromagnetic field. Charge can be Concave lens A lens that curves inward in
positive or negative. Similar charges repel; the middle. Also called a diverging lens. Convex lens A lens that curves outward in
opposite charges attract. the middle. Also called a converging lens.
Concentration A measure of the
Chemical Any element or compound, amount of particles of a substance Correlation A correlation between two
especially those produced or extracted when mixed with another substance. variables means that as one variable
in an industrial process. Water, iron, salt, For example, the concentration of changes, the other also changes in a
and oxygen are all examples of chemicals. carbon dioxide in air is about 412 predictable way. Correlation does not
particles for every million air particles. necessarily mean that changing one
Chemical change A chemical change variable causes the other to change.
occurs when atomic bonds are made Condensation The change of state when a
and broken in a chemical reaction. This gas turns into a liquid. Cosmic microwave background radiation
results in a new chemical substance (CMBR) Faint microwave radiation found
being formed. Conduction The movement of heat or throughout the Universe. It is thought to be
electricity through a substance. energy left over from the Big Bang.
Chemical energy The energy stored in the
bonds between atoms. It may be released Conductor A substance through which Cosmic rays Highly energetic particles,
during a chemical reaction, for example, as heat or electric current flows easily. such as electrons and protons, that travel
heat and light. Food, fuels, and electrical through space at close to the speed of light.
cells store chemical energy. Conservation of energy See Law of
conservation of energy. Coulomb (C) The unit of electrical charge.
Chemical reaction A process that changes One coulomb is the quantity of charge moved
substances into new substances by breaking Conservation of momentum See Law of in one second by a current of one amp.
and making chemical bonds. conservation of momentum.
Critical angle An angle of incidence greater
Circuit The path through which an electric Constant A quantity that does not vary, than the critical angle causes total internal
current can flow. symbolized by a letter in an equation. reflection (TIR) instead of refraction.
Constants usually represent a physical
Climate The pattern of weather and seasons property, such as how easily stretched a Crumple zone A safety feature in which
a place experiences in a typical year. spring is (spring constant). parts of a vehicle are designed to deform
(crumple) in a collision. This means that
Climate change Long-term changes Contact force Any force delivered through the vehicle decelerates over a longer
in Earth’s weather patterns. See also direct contact. Examples include air period of time, reducing the chance of
global warming. resistance, friction, and tension. serious injuries.

274

Crust (Earth) The thin, rigid outer surface Displacement 1. The straight line Electric field A region surrounding a
of Earth made of rock. distance between two points in a charged particle (such as an electron
particular direction (a vector quantity). or ion) in which other charged particles
Current (electric) A flow of charged Units are meters (m) or kilometers (km). experience a force.
particles such as electrons or ions. The 2. The moving aside of a medium by an
unit is the ampere (A). object placed in that medium, such as Electrical power The amount of electrical
bath water rising when a person gets in it. energy converted every second into other
Curve of best fit A smooth curve drawn forms of energy. It is measured in watts (W).
through the points on a graph that comes Dissipate The process by which
as close to as many of them as possible. something spreads out, becoming Electricity The effects caused by the
See also line of best fit. less concentrated as it does so and presence and/or movement of electric charge.
effectively disappearing. For example,
Dark energy A poorly understood force that heat escaping from a poorly insulated Electromagnet A coil of wire that becomes
acts in the opposite direction to gravity, house will dissipate into the atmosphere. magnetic when electricity flows through it.
causing the Universe to expand. About
two-thirds of the content of the Universe Diverging lens A lens that curves inward Electromagnetic induction The process by
is dark energy. in the middle. Also called a concave lens. which a voltage is induced in a conductor
Diverging lenses make parallel beams of when the conductor moves across a
Dark matter Invisible matter that can light spread out. magnetic field. If the conductor is part
only be detected by its gravitational of a complete circuit, then a current will
effect on visible matter. Dark matter Drag Another name for air resistance or flow in that circuit.
helps hold galaxies together. water resistance.
Electromagnetic radiation A form of
Data Information gathered in Dwarf planet A small, planetlike energy that travels at the speed of light,
an experiment. object that is massive enough to is a transverse wave, and can travel
have become rounded by its own through a vacuum.
Decay (radioactive) The process by which gravity but not massive enough
a radioactive atom’s nucleus spontaneously for its gravity to have cleared the Electromagnetic spectrum The complete
emits ionizing radiation, often transforming surrounding space of objects. range of electromagnetic radiation from radio
into a different element. waves to gamma rays. See also spectrum
Dynamo A generator that produces and visible spectrum.
Deceleration Slowing down. In this case, direct current.
the acceleration is in the opposite direction Electron One of the three main particles in
to the velocity. Efficiency A measure (usually a percentage) an atom (with the proton and neutron). It
of how much of a system’s input energy is has a negative charge.
Density The mass (amount of matter) converted into useful energy.
of a substance per unit volume. Units Electron shell One of the layers in which
are kg/m3 or g/cm3. Effort A force applied against a load, electrons are arranged outside the nucleus
such as the lifting force used to raise of an atom.
Dependent variable The variable that you a wheelbarrow.
measure in an experiment. Electrostatic force The force experienced
Elastic An object is elastic if it returns to its by a charged particle when it is in an
Diffuse reflection This occurs when light original size and shape after being stretched electric field.
is reflected in random directions from an or compressed.
uneven surface. Element A pure substance that cannot
Elastic collision A collision between be broken down into other substances
Diffusion The gradual mixing of two or objects that spring back into their by chemical reactions. Examples include
more substances as a result of the random original shape after impact, with no carbon, hydrogen, and oxygen.
movement of their particles. loss of kinetic energy.
Ellipse An oval shape like a flattened circle.
Diminished (of an image) An image that Elastic limit The maximum amount that a
is smaller than the object. material can be stretched or compressed Energy The capacity to do work.
and still return to its original shape. Energy can be stored and transferred
Diode An electronic component that in different ways. For example, energy
lets electricity flow in one direction only. Elastic potential energy The energy stored can be stored in the chemicals in a cell
in a stretched or compressed material, and transferred by electricity when the
Direct current (d.c.) An electric current sometimes called strain energy. This stored cell is put into a circuit.
that flows in one direction only. See also energy comes from the work done in
alternating current (a.c.). stretching or compressing the material. Energy resource A store or source of energy
that can be used.
Discrete variable A variable that may Electric current A flow of charged particles
only have certain values, such as months such as electrons or ions. The unit is Equilibrium A state of physical or
of the year. the ampere (A). chemical balance.

275

Evaporation A change of state in which a Friction A force that resists or stops the Global warming A rise in the average
liquid turns into a gas (vapor). movement of objects that are in contact temperature of Earth’s atmosphere
with one another. caused by increasing levels of greenhouse
Fair test A scientific experiment in which gases. One of the main causes is the
the only things that change are the Fulcrum The point around which an object burning of fossil fuels, which releases
independent and dependent variables. rotates. Also called pivot. the greenhouse gas carbon dioxide.

Farsighted Unable to see nearby Fuse A safety device used in electrical Gradient The steepness of a line. Gradient
objects clearly. Farsightedness can be circuits. It contains a thin wire that melts if is measured by dividing the vertical
corrected by wearing glasses with too much current passes through, breaking distance between two points on the line
converging lenses. the circuit. by the horizontal distance between these
same two points.
Field The region in which a noncontact g A measure of gravitational field strength.
force such as gravity or magnetism has The value for Earth is 9.8 N/kg, which Gravitational constant (G) More
an effect. causes falling objects to accelerate at commonly referred to as “big G,”
9.8 m/s2 in the absence of air resistance. this is a tiny number used in gravity
Field lines Lines in a diagram of a force field calculations. Its smallness tells us
that show the direction in which the force Galaxy A large collection of stars and that gravity is a very weak force that
acts. The field is strongest where the lines clouds of gas and dust that are held needs very massive objects to produce
are closest together. together by gravity. a noticeable gravitational field.

Fluid A substance that can flow, such as a Gamma decay A form of radioactive decay Gravitational field The space surrounding
gas or liquid. in which an atomic nucleus emits gamma an object with mass, in which another object
radiation—a dangerous, high-energy type with mass will experience an attractive,
Focal length The distance between the focal of electromagnetic radiation. gravitational force.
point of a lens and the center of the lens.
Gamma rays Electromagnetic radiation Gravitational field strength The force with
Focal point The point at which parallel rays with the highest energies, highest which a gravitational field pulls on a mass of
of light are focused by a converging lens or frequencies, and shortest wavelengths. It 1 kg. Units are N/kg. See also acceleration
the point from which rays of light appear to is emitted from the nuclei of decaying due to gravity.
have come from after passing through a radioactive atoms.
diverging lens. Gravitational potential energy (GPE)
Gas A state of matter in which the particles The energy that a body has as a result
Force A push or a pull. Forces change are far apart and move about randomly of its mass and position (usually height)
the speed, direction, or shape of objects. and quickly. in a gravitational field. Lifting an object
Force is a vector quantity, and the units increases its store of GPE.
are newtons (N). Gears Mechanical devices such as
interlocking cogs that make the turning Gravity A force of attraction between all
Force field The region in which a force can effect of a force bigger or smaller. Gears objects that have mass. Earth’s gravity
be detected. can make machines like cars move keeps our feet on the ground and makes
faster (but with less force) or slower objects fall when we drop them.
Force meter Also called a newton (with more force).
meter, a force meter is any device that Greenhouse effect The way in which gases
measures force. Geiger-Müller (GM) tube An instrument such as carbon dioxide trap heat in Earth’s
used to detect and measure radiation. atmosphere. The build-up of these gases
Fossil fuel A fuel derived from the It consists of two plates with a high leads to global warming.
fossilized remains of living things. voltage across them. Ionizing radiation
Coal, crude oil, and natural gas are causes a spark to jump between the Greenhouse gases Gases such as carbon
fossil fuels. plates, which is detected by circuitry dioxide and methane that absorb energy
in the instrument. This circuitry and reflected by Earth’s surface, stopping it
Free body diagram A diagram showing the GM tube are together called a from escaping into space.
all the forces acting on an object. The Geiger counter.
forces are represented by arrows showing Ground wire Also known as an earth wire,
the direction of the forces. Geocentric model A model of the a wire connected to the metal case of an
Universe with Earth at its center. appliance such as a tea kettle. If there is a
Freezing point The temperature at fault and the case becomes “live,” then
which a liquid turns into a solid. It is the Geostationary orbit A satellite in a large current immediately flows from the
same temperature as the melting point of geostationary orbit is positioned over case through the ground wire. This causes
the solid. the equator, moves in the same direction a fuse to melt or triggers a circuit breaker,
that Earth turns, and takes about 24 making the appliance safe.
Frequency The number of waves that hours to orbit Earth once. To an observer
pass a point every second. The units on Earth, the satellite appears stationary Grounded An electrical appliance is
are hertz (Hz). in the sky. grounded if it is connected to a ground wire.

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Half-life The time taken for radioactivity in Infrared radiation Electromagnetic Kelvin (K) A scale of temperature that
a sample to drop to half of its original value. radiation with a lower frequency and longer begins at absolute zero (−273°C). Its unit
In other words, the time taken for half the wavelength than visible light. Infrared of measurement is the kelvin. A rise or fall
radioactive atoms in the sample to decay. radiation transfers heat and is used by of 1 K is the same as a rise or fall of 1°C.
remote control devices for televisions.
Heat Energy stored in the movement Kilowatt (kW) A unit of power equal to
of atoms (vibrations for solids). Heat can Infrasound Sound with a frequency less 1000 watts.
be transferred by conduction, convection, than about 20 Hz. This sound cannot be
and infrared radiation. heard, as it is too low for the human ear Kilowatt-hour (kWh) A unit of energy
to detect. used by utility companies in energy bills.
Heliocentric model A model of the solar 1 kWh is the energy transferred when
system with the Sun at its center. Instantaneous speed The speed at a 1 kW appliance is used for 1 hour. 1 kWh
which an object is traveling at any is equal to 3 600 000 joules.
Hertz (Hz) The SI unit of frequency. particular moment. Speedometers on
One hertz is one cycle (one complete cars show instantaneous speed. See Kinetic energy The energy stored in an
wave) per second. also average speed. object because of its movement. Its
value increases with the object’s speed
Hooke’s law This law says that the Insulator A material that reduces or stops and mass.
deformation (stretching or squeezing) of a the transfer of heat, electricity, or sound.
material is proportional to the force applied Latent heat The energy transferred during a
to it. This law applies up to the elastic limit, Interference The process whereby two or change of state at constant temperature.
beyond which the material will not spring more waves combine, either reinforcing each Latent energy is absorbed when ice melts
back into its original shape when the force other or cancelling each other out. and when water boils but is released when
is removed. steam condenses and when water freezes.
Internal energy The total kinetic and
Hypothesis An educated guess or idea about potential energies of all the particles Law of conservation of energy A law stating
how something works. Scientists test their in a system. that you cannot create or destroy energy.
hypotheses by carrying out experiments. Energy can only be stored or transferred.
Inversely proportional If two variables (such
Incident ray The ray of light that enters a as pressure and volume of a fixed amount of Law of conservation of momentum A law
lens or shines upon (“is incident upon”) gas in a container) are inversely proportional, stating that the total momentum of a system
a mirror. then as one increases, the other decreases before and after a collision remains constant
in such a way that their product (pressure × as long as no outside resultant forces are
Independent variable The variable volume) remains constant. For example, if acting on the system.
in an experiment that is deliberately you double the pressure of a gas at constant
changed so its effect on the dependent temperature, then the volume will halve. Law of reflection This law says that when
variable can be measured. light is reflected from a plane (flat) mirror,
Inverted image An image that is upside the angle of incidence equals the angle of
Induced magnet A material that becomes down in comparison with the object reflection.
temporarily magnetized when placed in a being viewed.
magnetic field. For example, the iron core LED Light-emitting diode. An electrical
of an electromagnet becomes an induced Ion An atom (or group of atoms) that has component that only allows current to flow in
magnet when the electromagnet is lost or gained one or more electrons and so one direction and that emits light when
switched on. become electrically charged. current flows through it.

Industrialization The widespread Ionizing radiation Radiation (nuclear or Lens A curved, transparent piece of
development of industries in a country, electromagnetic) with enough energy to plastic or glass that can bend light rays
often leading to the growth of cities and remove the electrons from the outer shells using refraction.
road or rail networks. of atoms to form ions.
Lift The upward force produced on a wing
Inelastic collision A collision in which Irradiated An object or material that has when it moves through the air.
kinetic energy is lost and the colliding been exposed to ionizing radiation.
objects change shape permanently. A Light Electromagnetic radiation that our
collision between cars is inelastic. See Isolated system A system that matter and eyes can see. White light is a mixture of all
also elastic collision. energy cannot leave or enter. the colors of the rainbow, which together
make up the visible spectrum. Some
Inertia The tendency of an object to keep Isotopes Forms of an element that have scientists use the term “visible light” for
moving in a straight line or remain at rest different numbers of neutrons in the atomic radiation our eyes can see and “light”
until a force acts on it. nucleus but the same number of protons. for all kinds of electromagnetic radiation.

Inertial mass A measure of how difficult it Joule (J) The unit of energy, equal to the Light-dependent resistor (LDR) A
is to change the velocity (speed and/or work done by a force of 1 N moving 1 m in component whose resistance increases or
direction) of an object. the direction of the force. decreases in a predictable way when the

277

amount of light that it absorbs changes. 2. The two points on Earth toward which Motor A machine that uses electricity
LDRs are useful in control systems—for a compass needle points. and magnetism to produce motion that is
example, in automatically turning street usually rotational.
lights on when it gets dark. Magnetism The property of some
materials, especially iron, to attract or Nearsighted Unable to see distant objects
Light-year A unit of distance used in repel similar materials. clearly. Nearsightedness can be corrected
astronomy. One light-year is the distance by wearing glasses with diverging lenses.
traveled by light in one year, equal to Main sequence star A star in the middle of
9.46 trillion km (9.46 × 1015 m). its life. A main sequence star, like our Sun, Nebula A huge cloud of dust and gas in
emits energy by fusing hydrogen into heavier space in which new stars may form.
Limit of proportionality If you stretch a elements such as helium.
material beyond this point, then Hooke’s law Net force When you add up the forces
won’t apply. The relationship between force Mantle (Earth) The large part of Earth’s on an object and take into account their
and extension is no longer a straight-line interior between the outer core and the directions, the result is a single force that
graph (linear); it becomes curved (nonlinear). crust, made of rock. would have the same effect, called the net
force or resultant force.
Line of best fit A line drawn through Mass The amount of matter in an object,
scattered data points on a graph so that it measured in grams, kilograms, or tons. Neutral wire The wire that completes the
comes close to as many of them as possible. Mass and weight are not the same. circuit in electrical circuits. It is usually kept
Drawing a line of best fit helps identify the Weight is the gravitational force between at zero volts.
relationship between the independent and Earth and the object with mass being
dependent variables. considered. Neutron One of the two main particles in
the nucleus of an atom. It has no electric
Linear relationship Two variables have Mass number Also called the nucleon charge and a relative mass of 1.
a linear relationship if the graph of this number, the total number of protons and
relationship is a straight line. For example, neutrons in the nucleus of an atom. Newton (N) The unit of force.
a material that obeys Hooke’s law shows a
linear relationship between the force applied Matter Anything that has mass and Newton meter (Nm) The unit of the
to it and the extension. occupies space. moment of a force.

Liquid A state of matter between a solid Medium The matter through which a wave Noncontact force Any force that acts at a
and a gas in which the particles can slide is traveling. distance. Noncontact forces include gravity,
around but remain close together and magnetism, and electrostatic forces.
attract one another. Megawatt (MW) A large unit of power
equal to 1 million watts (106 W). This Nonlinear A relationship between two
Live wire The wire in an electrical circuit unit is commonly used in describing variables that is not a straight line on a
that carries the electric current. electricity generation. graph. For example, if you double the
current flowing in an electrical device, then
Load The total force pushing on an Melting point The temperature at the power of the device rises by four times.
object or opposing the movement of which a solid turns into a liquid. It is
an object, such as the weight of heavy the same temperature as the freezing Nonrenewable resource A resource that will
material in a loaded wheelbarrow. point of the liquid. eventually run out, such as coal, oil, or gas.

Longitudinal wave A wave in which particles Microwaves Electromagnetic waves with Normal A line drawn at 90 degrees to the
vibrate back and forth along the direction of a wavelength longer than that of infrared plane of a mirror or lens. Angles of light rays
travel of the wave. rays but shorter than that of radio waves. are measured from this line.
Microwaves are sometimes said to be a
Lubrication Using oil or other lubricants to type of radio wave. Normal force The part of a contact force
reduce friction. that acts at 90 degrees to the surface
Molecule A particle of matter made of two being considered.
Luminous A luminous object emits its own or more atoms strongly bonded together.
light—for example, a candle or a star. Nuclear energy 1. Energy stored in
Moment Also known as torque, the the bonds between the particles in an
Magnet Any object that produces a turning effect of a force, such as a atomic nucleus. This may be released
magnetic field. wrench turning a nut. The moment by nuclear fusion or nuclear fission.
of a force is calculated by multiplying 2. Electricity generated by a nuclear
Magnetic field The space around a magnet the force by its perpendicular distance power station.
where it can affect magnetic materials. from the pivot. The unit is the newton
Magnetic fields decrease in strength as meter (Nm). Nuclear equation Similar to a chemical
you move farther from the magnet. equation, a nuclear equation describes the
Momentum The tendency of an object to changes that take place during nuclear
Magnetic poles 1. The two ends of a keep on moving, equal to its mass times its reactions such as fission, fusion, and
magnet, called the north and south poles. velocity. Units are kg m/s. radioactive decay.

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Nuclear fission A process in which Particles Basic units from which all Pressure The force per unit area. For
the nucleus of an atom splits into two substances are made, such as atoms or example, the pressure exerted by you on
smaller nuclei, releasing energy. molecules. Subatomic particles are those the ground is equal to your weight divided
smaller than an atom, such as protons. by the total area of your soles and heels.
Nuclear fuel The fuel for nuclear The units are N/m2 or pascals (Pa).
reactors. Most commonly, this is Pascal (Pa) The unit of pressure. 1 Pa is a
enriched uranium (uranium-235), force of 1 N spread over an area of 1 m2. Prism A triangular wedge of glass or
but some reactors use other fuels, other transparent material that can split
such as plutonium or thorium. PET scanner A machine used in medicine white light into a spectrum of colors.
to form images of processes in the body to
Nuclear fusion A process in which help diagnose diseases. PET stands for Proportional Two variables are proportional
atomic nuclei fuse (join) to form positron emission tomography. to each other if their graph is a straight line
heavier nuclei, releasing energy. through the origin. If one variable is
Stars such as the Sun are powered Photogate A device that detects moving multiplied by a number, the other variable is
by the fusion of hydrogen nuclei to objects when they pass between a source also multiplied by the same number (so
make helium. of light and a light sensor, allowing precise if one doubles, the other doubles, too).
measurements of time to be taken.
Nuclear power station A power Proton One of the two main particles found
station in which energy released by Physics The scientific study of force, in the nucleus of an atom. It has a relative
nuclear fission reactions is used to motion, matter, and energy. mass of 1 and a charge of +1.
generate electricity. This energy is
used to heat water to make steam, Pivot The point around which an object Proton number Sometimes called the
which is used to drive generators to rotates. Also called fulcrum. atomic number, the number of protons
produce electricity. in an atom’s nucleus. Each element has
Plane A flat surface. a different proton number.
Nucleon A proton or a neutron; in other
words, any particle in an atom’s nucleus. Plate tectonics The theory that explains Radiation An electromagnetic wave or
volcanoes, earthquakes, and other geological a stream of particles from a source of
Nucleon number The total number of phenomena. It says that the surface of Earth radioactivity.
protons and neutrons in the nucleus is divided into large plates that are able to
of an atom. Also called mass number. move against each other. Radio waves The longest wavelength,
lowest frequency, and lowest energy
Nucleus (plural nuclei) The center Position–time graph A graph that form of electromagnetic radiation. Uses
of an atom, made up of protons and represents a journey with distance on the include communication and radar.
neutrons. It contains most of the vertical (y) axis and time on the horizontal
atom’s mass. (x) axis. The slope of the line at any point is Radioactive A material is radioactive if it
the speed at that moment. contains unstable atomic nuclei that decay
Ohm (Ω) The unit of electrical resistance. into smaller nuclei, releasing ionizing
Potential difference Also called voltage, the radiation as they do so.
Orbit The path of a body around another, difference in electric potential between two
more massive body, such as the path of points. Potential difference can be thought of Radiotherapy The use of radioactive
Earth around the Sun. as providing the “push” that makes electric materials to treat cancer by destroying
current flow. It is measured in volts (V). cancerous body tissue. This radioactivity
Oscillation A regular movement back may be focused on a very small spot in
and forth. Potential divider An electric circuit that the body so there is minimal damage to
uses resistors in series for controlling the healthy surrounding areas.
Oscilloscope An instrument that shows voltage supplied to a parallel branch in
electrical signals on a screen. It is often the circuit. One of the resistors is usually a Ray diagram A diagram that represents
used to help us visualize waves, such as component such as an LDR or thermistor. light rays and how they are affected by
sound waves. lenses or mirrors.
Potential energy Energy stored in the
Outlier An item of data that does not shape or position of something. Gravitational Real image An image formed when light rays
fit the pattern of the other data points. potential energy is the energy stored in an are focused on a surface such as a screen.
Outliers are usually errors but may object because of its height. Elastic potential
sometimes reveal something unexpected energy is stored in objects when they are Red giant A late stage in a star’s life when
about a system. Ideally, an experimenter stretched, squeezed, or twisted. hydrogen in the star’s core has been
will return to the experiment and try to converted to helium, the core has collapsed,
measure the outlier again. Power A measure of how quickly energy and outer parts of the star have cooled and
is transferred. For example, a bulb with a greatly expanded, forming a large, red star.
Parallel (electrical circuits) Components power rating of 100 W converts 100 J of
connected in parallel are connected side electrical energy every second into heat Red supergiant An aging star similar to a
by side in parallel branches rather than and light energy. The unit of power is red giant but on a much larger scale. These
in a line (in series). the watt (W). are the largest stars in the Universe.

279

Redshift The apparent stretching of light Semiconductor A material partway an atom, to radio waves, whose wavelengths
waves from distant galaxies into longer between an electrical conductor (such may be many kilometers long. The visible
wavelengths. This is strong evidence that as a metal) and an insulator (such as spectrum is the part we can see.
these galaxies are moving away from us glass). Semiconductors are used in
and from each other, which indicates most electronic circuits. Speed The distance traveled in a particular
that the Universe is expanding. time. Speed is a scalar quantity and does
Series (electrical circuits) Components not have a direction. Units are m/s, km/h,
Refraction The bending of a wave as it connected in succession in an electrical or mph. See also velocity.
speeds up or slows down on moving from circuit are described as being in series.
one medium to another. Refraction of light The same current flows through all of Split-ring commutator A device in electric
makes a stick placed in water look bent at them. See also parallel. motors that reverses the electric current in
the point it enters the water. the rotating coil at every half-turn of the coil.
SI unit The standard, agreed This means that the electromagnetic force
Regular reflection Reflection of light off international units for physical acting on the coil is always pushing the coil
a smooth surface, such as a mirror. measurements. For example, the in the same direction.
SI unit for mass is the kilogram. SI
Relative mass The mass of a particle or stands for Système International. Spring constant A number describing the
molecule in comparison to one-twelfth of strength of a spring, usually represented
the mass of a carbon-12 atom. It is a useful Significant figures The number of figures by the letter k. The greater the spring
unit when working with very small masses. (digits) that an experimenter considers constant, the more force is needed to
Carbon-12 is chosen as a standard for accurate in a measurement. For example, stretch the spring. The units are N/m.
convenience and historical reasons. Protons if timing a 100 m sprinter by hand with
and neutrons have a relative mass of 1. a stopwatch, including hundredths of a Standard form Also called scientific
second would not be reasonable, as a human notation, a way of abbreviating very
Renewable energy A source of energy cannot be that accurate. Three significant large or small numbers. The significant
that will not run out, such as sunlight, figures in this case would be sufficient (two figures are written with a decimal point
wave power, or wind power. for seconds and one for tenths of a second). after the first figure, followed by the power
of 10 this needs to be multiplied by. For
Repeatable (experiment) An experiment Solenoid A cylindrical coil of wire that example, the speed of light, which is
is repeatable if making the same becomes a magnet when an electric current about 300 000 000 m/s, can be written
measurement with the same equipment is passed through it. as 3.0 × 10 8 m/s.
gives the same result.
Solution A mixture in which the Standing wave A standing wave forms
Reproducible (experiment) An experiment molecules or ions of a substance are when a wave interferes with its own
is reproducible if someone else follows your spread out in a liquid. For example, salt reflection, resulting in peaks and troughs
method with different equipment and gets water is a solution. that do not move. Waves formed in the
the same result. bodies and strings of musical instruments
Sonar Sound navigation and ranging. A are standing waves.
Resistance A measure of how much a method of detecting objects underwater by
material opposes the flow of electric sending out sound waves and interpreting Star A massive ball of incandescent gas
current. The units are ohms (Ω). their echoes. inside which nuclear fusion produces large
amounts of electromagnetic radiation. The
Resultant force When you add up the Sound A kind of wave that travels through fusion processes in stars produce nearly all
forces on an object and take into account matter, alternately squeezing particles the chemical elements in the periodic table.
their directions, the result is a single force together and then pulling them apart. Sound
that would have the same effect, called the waves in air are detected by the human ear. States of matter The different physical
resultant force or net force. forms that matter can take, such as solid,
Specific heat capacity The amount of liquid, and gas.
Sankey diagram A diagram that uses energy it takes to heat 1 kg of a substance
arrows of different widths to represent the by 1°C. The same quantity of energy is Static electricity An electric charge held
quantity of energy flowing into a system released when 1 kg of the substance cools on an object, caused by the gain or loss
and the useful and wasted energy leaving by 1°C. Units are J/kg °C. of electrons.
it. It is useful in showing and calculating
the efficiencies of devices. Specific latent heat The amount of Stopping distance The total distance
energy taken in or released when 1 kg traveled between a driver seeing a
Scalar A quantity that has a magnitude of a substance changes state without a hazard on the road and the car stopping.
(size) but no direction. Mass and change of temperature. The units are Stopping distance = thinking distance +
temperature are scalar quantities. J/kg. See also latent heat. braking distance.
See also vector.
Spectrum (electromagnetic) The range Streamlined Shaped to reduce the force
Seismic wave A wave that travels of the wavelengths of electromagnetic of air or water resistance. Streamlined
through Earth from an earthquake, radiation. The full spectrum ranges from objects are usually narrow, with smooth,
large explosion, or other source. gamma rays, with wavelengths shorter than tapering shapes.

280

Subatomic particle A particle that is smaller Total internal reflection Reflection of light Velocity A measure of an object’s speed
than an atom, such as a proton, neutron, within a medium such as glass or water when and direction. Velocity is a vector quantity.
or electron. the angle of incidence is greater than a certain The units are m/s or km/h.
critical angle, resulting in an angle of refraction
Sublimation A change of state from solid more than 90°. Total internal reflection is used Vibration Rapid back-and-forth movement.
straight to gas without becoming a liquid. to trap light in fibre-optic cables. Musical instruments use vibration to
generate sound waves.
Supernova An explosion caused by the Transformer A device that uses
collapse of a massive star. A supernova may electromagnetic induction to increase or Virtual image An image formed where
be many billion times brighter than the Sun. decrease the voltage of an alternating light rays appear to be focused, such as
The vast energies of supernovas are enough electricity supply. a reflection in a mirror. Virtual images
to produce elements heavier than iron by cannot be projected on a screen.
nuclear fusion. Transverse wave A wave in which the
particles of the medium vibrate at right Visible spectrum The range of
System The environment in which physical angles to the direction in which the wave electromagnetic waves that we can
phenomena being studied exist. For example, travels. Waves on water are transverse. see. The visible spectrum can be
in studying gases, we may choose a cylinder divided into seven colors: red, orange,
and piston as the system, but for studying Turbine A machine with blades like a fan yellow, green, blue, indigo, and violet.
climate change, it may be the entire planet. that spins when air or liquid flows through it.
Turbines are used to drive the generators in Volt (V) The unit for potential
Systematic error An experimental error power stations. difference (voltage).
typically caused by faulty equipment, such
as a balance that has not been zeroed Ultrasound Sound with frequencies Voltage A common term for electrical
correctly. This type of error is nonrandom above 20 000 Hz, which are too high potential difference.
and makes every measurement wrong by for humans to hear.
the same amount. Voltmeter A device used to measure
Ultraviolet (UV) light Electromagnetic potential difference (voltage).
Temperature A scientific measure of how radiation with a shorter wavelength than
hot or cold something is. Temperature is a visible light. Higher-energy UV radiation Volume The amount of space an object
measure of the average kinetic energy of is ionizing and can cause sunburn or takes up. The units are m3 or cm3.
particles in a system but not total internal even cancer. Uses of UV include security
energy. The units are °C (degrees Celsius) marking and disinfection. Water resistance A force that resists the
or K (kelvin). movement of objects through water. Like air
Unbalanced forces Unbalanced forces resistance, it always acts in the opposite
Tension When forces pull an object in produce a resultant (net) force on an direction to the object’s motion.
opposite directions, the object is in tension. object, causing acceleration or deformation
(squashing or stretching). Watt (W) The unit of power. 1 watt = 1 joule
Terminal velocity The maximum velocity per second.
a falling object reaches when the force Universe The whole of space and
of air resistance balances the force of everything it contains. Wave Sound, light, and other energy transfers
gravity pulling it downward. For example, travel as waves—regular oscillations that
when the air resistance experienced by Unstable isotope An isotope whose spread out rapidly through matter or space.
a parachutist becomes equal to their atomic nuclei are likely to break down
weight, they stop accelerating and fall and release radiation. Wavelength The distance between two
at terminal velocity. successive peaks or two successive
Upthrust The upward force exerted by a troughs in a wave.
Tesla (T) The unit of magnetic flux density. liquid or a gas on an object within it.
It is closely related to the strength of a Weight The force due to gravity felt by any
magnetic field. Uranium A radioactive element used as the object with mass. Weight is a force, so the
fuel in nuclear power stations or as the units are newtons (N).
Thermal image A picture produced using active component in an atomic bomb.
infrared radiation rather than visible light, White dwarf The very hot, small, dense
with colors representing temperature. Vacuum A space in which there is no matter. remains of a dead star.
Hotter objects are usually depicted as
redder and colder objects as bluer. Variables Things that might change in an Work The energy transferred when a force
experiment. Variables can be independent moves an object in a particular direction.
Thermistor A resistor whose resistance (the things you change), dependent (the The units are joules (J).
changes with temperature. thing you measure), or controlled (things
you must keep the same). X-ray Electromagnetic radiation with high
Thinking distance The distance traveled by energy and frequency and very short
a vehicle between a driver seeing a hazard Vector A quantity that has both magnitude wavelength. X-rays can penetrate most
on the road and pressing the brake. It (size) and direction, such as a force. See matter, which makes them useful for
depends on the reactions of the driver. also scalar. making images of bones and teeth.

Circuit symbols 281

Switch Switch Cell Battery
open (off) closed (on) Thermistor
Variable
Bulb Resistor resistor Fuse

LDR Diode LED
(light-dependent M
V
resistor) Voltmeter Motor

A
Ammeter

282

Index

Page numbers in bold refer to atoms carbon 269 collisions
main entries. atomic model 239 car safety features 107
atomic structure 237 atoms 237 elastic and inelastic 102–103
AB electromagnetic waves 148, momentum 100, 101
149 isotopes 238
absolute magnitude 271 elements and isotopes 238 carbon capture and storage 40 resistance 163, 164
absolute zero 232 ions 241 carbon dioxide 38, 39, 252
absorption nuclear fission 250–251 color
nuclear fusion 253 cars
infrared radiation 43–45 nuclear medicine 248–249 and absorption of infrared
light 128, 147 radioactive decay 240–244 acceleration 97, 99
sound 128 static charge 190 radiation 43, 44–45
acceleration 68–69, 98–99 braking distance and energy
gravity 55, 73 attraction 93, 197 108–109 electrical wiring 180
Newton’s second law 97 by induction 190
terminal velocity 110–111 magnetism 196 inelastic collisions 103 iridescence 125
velocity 66, 67 static electricity 188–189, 194 and light 145–146
velocity–time graphs 70–71 motors 201 of stars 271
accuracy 26 aurora 149 safety features 107 color filters 147
action–reaction forces 92, 93 average speed 62 speed and safety 109 comets 259, 262
aerogel 46 axis of rotation 256–257 communications 150
air axles 91 stopping 104–106 compasses 197, 198
atmospheric pressure 228 background radiation 245 component forces 78
convection currents 48–49 balance cells (electrical) 154 compression 83, 212
refractive index 138, 139 springs 80, 81
sound waves 114, 117, 120 center of mass 86–87 cells (human) 246
air pressure 208, 235 principle of moments 85 computational models 16
air resistance 53, 68, 73, 74, balanced forces 75, 92, 110–111 central heating systems 48
bar charts 22 center of mass 86–87 computers 185
106 barometers 231 centrifugal force 96 concave lenses 140, 141, 144
and terminal velocity 110–111 base units 30 centripetal force 96, 262 concentration 214
alpha decay 243 batteries 154, 179 chain reactions, nuclear 251, 252 conclusions 11, 25
alpha particles 239, 240, 241, becquerels 240 charge, electric 156–157, 160, 173 condensing 213, 224, 225
bending 83 conduction 42, 46, 50, 51
243, 246 beta decay 243 electric fields 194 conductors, electrical 153, 185
alpha radiation 247, 249 beta particles 241, 243, 246 static electricity 188–189
alternating current (a.c.) 150, beta radiation 247 chemical energy 34, 35, 38 ohmic and nonohmic
Big Bang theory 265, 266 circuit breakers 181
170, 179, 206, 209 biofuels 14, 36, 40 169, 170
alternators 206 black dwarfs 269 circuit diagrams 154 conservation of energy 35, 54
altitude, atmospheric pressure black holes 268, 269 circuit symbols 272 conservation of mass 212
blue hypergiants 270 circuits, electrical 153, 154, conservation of momentum 100,
228 blue supergiants 270
ammeters 156, 162, 205 blueshift 265 155–177 102, 103
amplitude 113, 115, 124, 128 Bohr, Niels 239 changing resistance 161 constructive interference 124
amps 156 boiling 213, 223, 224 charge 160 contact forces 73
Andromeda galaxy 13, 263 brain circuit breakers 181 contamination, radioactive 246
angle of incidence 130, 132, scanning 249 circuit symbols 272 continuous variables 23
sound 118 control variables 18, 19, 44
133, 134, 135, 139 vision 136 current and voltage calculations convection 42, 48–49, 50, 51
angle of reflection 130, 132 brake disks 109 167–168 converging lenses 136, 140,
angle of refraction 133, 139 brakes 55
antennae 150 braking distance 105–106 current and voltage graphs 141, 142–143
apparent magnitude 271 and energy 108–109 169–170 convex lenses 136, 140, 141,
appliances Brown, Robert 214
Brownian motion 214 light-dependent resistors 174 142–143
domestic 184 Bunsen burners 17 measuring electricity 156–157 cooling 224
electrical 183 buoyancy 230 power in 171
asteroids 258, 259 rectifier 170 by evaporation 218
astronomer 12–13, 264, 265 C relays 201 Copernicus, Nicolaus 12
atmosphere resistance in wires 162–164
climate change 38, 39 calculators 21 core, Earth’s 255
Earth’s 255 cameras 136 resistors in series and parallel correlation 24
giant planets 259 165–166 cosmic microwave background
Sun’s 261 pinhole 129
atmospheric pressure 228, 229, cancer 151, 246, 248–249 sensor 176–177 radiation 267
series and parallel 155, 158–159 cosmic radiation 245
231 thermistors 175
atomic mass 216 circular motion 96 coulombs 160
atomic number 238, 242, 243
circular orbits 262 Crab Nebula 264
cranes, tower 56, 85
cleaning, ultrasonic 121 crash tests 107
climate change 14, 36, 38, 39, critical angle 133, 134, 135, 139
crumple zones 107
40
crust, Earth’s 255
clouds 49, 213 current electricity 153, 154–177
coal 38, 40
calculating energy 172–173
cochlea 118
current and voltage calculations
coils 167–168

generators 206, 207

magnetic fields 199, 204, 205,

208

transformers 209, 210

283

current electricity continued displacement continued electricity continued energy continued
current and voltage graphs and upthrust 230 energy-efficient devices 41 and food 33
169–170 fuses and circuit breakers 181 forces and transfer of 55
direct and alternating current distance generators 206–207 heat transfers 42
179 and magnetism 199 internal 218
electric motors 204 and acceleration 69 measuring 156–157 kinetic and potential 52–53
electromagnetic induction 205 nuclear power 252 nonrenewable 38
electromagnets 199 calculating 62 power transmission 186
fuses and circuit breakers 181 preventing shocks 182 nuclear fission 250–251
generators 206–207 and displacement 66 renewable energy 34, 36–37
motor effect 202–203 measuring 20, 63 nuclear fusion 253
power in circuits 171 position–time graphs 64–65 safety 17 and power 56–57
power transmission 186 static 188–194 power in circuits 171
preventing shocks 182 sonar and echolocation 122 transformers 209–210 radiation 43–45
transformers 209–210 using 179–186 reducing energy transfers 50–51
in space 263 wasted energy 185 renewable 14, 36–37
currents, convection 48–49, 220 see also circuits, electrical; stores 34
and speed 61 trends in energy use 40
DE stopping 105–106 current electricity; use in the home 184
wasted 41, 185, 186
Dalton, John 239 transfer of energy by forces 55 electromagnetism; static energy consumption 40
dark energy 266 diverging lenses 140, 141, 144 energy stores 32, 34, 35, 52–53
dark matter 266 electricity energy transfers 32, 35
data diving 229 by forces 55
electromagnetic energy 153 calculating 172–173
analysis 11 DNA 246 calculating efficiency 58–59
collecting 10, 19 electromagnetic induction 109, conservation of energy 54
patterns in 24 domestic appliances 184 205, 206, 208 efficiency 41
presenting 22–23
quality 29 double-glazing 51 electromagnetic radiation 13, 43, electrical appliances 183
recording 21 148–149, 151, 241, 264, 265
deceleration 55, 69, 73 drills, electric 204 electromagnetic waves 148, 151
see also stopping distance; electromagnetic spectrum 13, energy stores 34
driving 15, 105–106 148–149, 264 heat transfers 42, 223
terminal velocity drogue parachutes 69
deformations 83 dwarf planets 259 electromagnetic waves 13, 42, inelastic collisions 103
dynamos 206, 207 148–149, 151
elastic and inelastic 80, 81 ears 118 kinetic and gravitational energy
density 216 electromagnetism 199–210 52–53
Earth electromagnets 199–200
and buoyancy 230 atmospheric pressure 228 power 56–57
finding 217 circuit breakers 181 reducing 50–51
and pressure 229 background radiation 245 wasted energy 185
dependent variables 18, 19 climate change 39 power station generators 207
deposition 213 eclipses 261 uses of 201 waves 113
depth, and pressure 229 gravity 93, 94 electronic instruments 20, 21
derived units 30 inner structure 123 electrons environment, background
descriptive models 16 magnetic field 198 radiation 245
destructive interference 124 Moon 260 atomic structure 237, 239
diamonds 138, 139, 238 equations 28–29, 273
diaphragms 208 planetary motion 12 charge 160, 190, 237
diffuse reflection 130 equinoxes 256
diffusion 214 rotation of 260 current electricity 153 errors 26
diodes 169, 170 seasons 256–257 free 163, 164, 170, 241
direct current (d.c.) 170, 179, ionizing radiation 241 ethics 14
solar system 258 evaluations 27
206, 207 structure of 255 metals 46
direction Earth-based telescopes 264 evaporation
earthquakes 123 radio waves 150 and boiling 224
of electrical current 179, 206,
207 echoes 122, 128 static electricity 190 changes of state 213, 216, 224
echolocation 122 cooling by 218
of forces 55, 73, 75, 92, 202 eclipses 261 electrostatic force 74
of light 129 efficiency, energy 41, 58–59 electrostatic paint sprayers 191 exercise
momentum 101 effort 88 elements and energy 33
vectors 66
velocity 67 Einstein, Albert 214 atoms 238 and health 15
of waves 113, 114 elastic collisions 102 formation in stars 269
discrete variables 23 elastic deformation 80, 81, 83 radioactive decay and formation exosphere 255
disease, diagnosing 248–249
displacement elastic limit 81 of 240, 242 expansion joints 215
and density 217 elastic potential energy 34, 55,
and distance 66, 69, 70, 71 elliptical galaxies 263 experiments
80, 81
electric fields 194 elliptical orbits 12, 262 conclusions 25
electric motors 204 energy 32 data 22–24
evaluations 27
electrical energy 34, 41 calculating efficiency 58–59
calculating electrical 172–173 and hypotheses 11
electrical impulses 118 charge and 160 measurements 20–21, 26
climate change 39 planning 18–19
electricity conduction 46 safety 17
appliances 183 conservation 54
calculating energy 172–173 consumption 40 scientific method 10, 11
charge 160 convection 48–49
current 153, 154–177 dark 266 scientific models 16
direct and alternating current 179 efficiency 41 explosions 103
electrical circuits 153–177 and expansion of the Universe
electrical wiring 180 extension 80, 81, 82
267
and energy transfers 35
energy use at home 184

284

eyes frames of reference 67 galaxies 263 infrared radiation continued
correcting vision 141 free body diagrams 76–77 gravitational field 93 emission 13, 42, 44–45, 148
lenses 136 free electrons 163, 164, 170, law of 94
vision 127 Moon 260 infrasound 118
241 rocket power 5 inkjet printers 191
F freezing 213, 216, 224 stars 268, 269 instantaneous speed 62
frequency Sun 258, 262
falling objects 110–111 and weight 79 insulation
farsightedness 141 electromagnetic radiation greenhouse effect 39
field lines 197 148–149, 151 ground wires 180, 182 electrical wiring 180, 182
fields grounding 191
iridescence 125 habitats 14 energy transfer 18–19, 47,
electric 194 light and color 145 half-life 244, 246 50–51
forces 93 light waves 128, 137 harmonic motion 54
see also magnetic fields radio waves 150 hearing 118 insulators 46–47
filament bulbs 163, 169, 170 sonar 122 heat electrical 153, 164
fireworks 117 sound waves 116, 118, 120, convection 48–49
fission, nuclear 250–251, 252 and energy transfers 35, 42, static electricity 188–189
Fleming’s left-hand rule 202, 121, 122, 128 interference 124–125
ultrasound 121, 122 218 internal combustion engines 235
203 waves 113, 116–117, 119 from Sun 257 internal energy 218
floating 230 friction 53, 55, 73, 74, 76 heating curves 223 inverse proportion 24, 94, 233
fluids air resistance 110–111 latent 223, 224, 225 inverse square law 94
and energy efficiency 59 specific heat capacity 219–222 ionizing radiation 151, 241, 246,
convection 48–49 fulcrums 88 wasted energy 41, 185, 186
measuring pressure in 231 fuses 181, 183 heat energy 41, 183, 219 247, 248
particles in 214 fusion, nuclear 253 heat expansion 215
focal length 140 heat loss 50 ionosphere 150
focal point 140, 142, 143, 144 GH heat transfers 42
focus 136 heliocentric model 12 ions
food galaxies 13, 263, 265 helium 269
electrical appliances 183, 184, expanding Universe 266, 267 hemispheres, Earth’s 256–257 atomic structure 237, 241
Herschel, William and Caroline 13
185 galaxy clusters 266 hertz 116 dissolved 153
energy 33 Galilei, Galileo 12 Hertzsprung, Ejnar 271
irradiating 247 gamma radiation 148, 149, 151, Hertzsprung-Russell diagrams resistance 163, 164
supply 14 iridescence 125
force meters (newton meters) 79, 241, 246, 247, 248, 249, 250 270, 271 iron 196, 198, 199, 200, 209,
gas, natural 38, 40 homes
80 gases 212, 213, 214, 216 269
forces 73 electrical appliances 183 irradiation 246
compression 228 energy use at 184 irregular galaxies 263
and acceleration 97–99 condensing 224 Hooke’s law 80, 81 isotopes 238
action–reaction 92 latent heat of vaporization 225 hot-air balloons 215 joules 33, 55, 171, 184
balanced and unbalanced 75 pressure 231, 232–234 houses, insulation 50–51 jumping wire 202
center of mass 86–87 work and temperature 235 Hubble, Edwin 13, 266 Jupiter 259
centripetal and centrifugal 96 gears 90 Hubble Space Telescope 264
deformations 83 Geiger-Müller tubes 240, 245 hydroelectric power 34, 36 Kelvin (K) scale 232
and energy transfers 35 generators 34, 37, 206–207 hydrogen 269
fields 93 Van de Graaff 189 hypotheses Kepler, Johannes 12
floating and sinking 230 genetic engineering 14 scientific method 10–11
law of gravity 94 geocentric model 12 testing 18, 19, 27 kilojoules 33
levers 84, 88–89 geostationary orbits 262 kilowatt-hours 184
magnetism 196 geothermal energy 37 IJKL kinetic energy 32, 52–53
mass and weight 79 giant planets 259
measuring 20 glass, refractive index 138, 139 ice 213, 216 braking distance 108–109
moments 84–85 gliders 49 melting 223, 225 elastic and inelastic collisions
momentum 100–101, 104 graphite 252
and motion 96–111 graphs incident rays 132, 142, 144 102–103
motor effect 202–203 current and voltage 169–170 independent variables 18, 19
resolving 78 data collection 19 induction energy stores 34, 54, 55
resultant 76–77 distance–time 64–65
simple machines 88–91 heating curves 223 attraction by 190 generators 206
springs 80–82 mathematical models 28 electromagnetic 205
surface pressure 227 presenting data 22–23 induced magnets 196 nuclear fission 250
transferring energy by 55 velocity–time 70–71 inelastic collisions 102, 103
types of 74 gravitational field 93, 94, 229 inelastic deformation 80, 81 and temperature 218, 232,
vectors 66 gravitational potential energy 34, inertial mass 97
fossil fuels 15, 38, 40 infrared radiation 264 234, 235
reducing use of 14, 36, 40, 50, 52–53, 54 absorption 43, 44–45
gravity 13, 73, 74 lasers 134
51, 252 latent heat 223, 224, 225
and acceleration 55, 68 Leavitt, Henrietta Swann 13
Earth 255
lenses
converging 140, 142–143
correcting vision 141
diverging 140, 144
refraction 131

levers 84, 88–89
light 127

atoms and 239
and color 145–146
comparing with sound 128
converging and diverging lenses

140
converging lens ray diagram 142
correcting vision 141
electromagnetic radiation 13,

148–149

285

light continued magnetic fields continued mesosphere 255 nuclear fission 250–251, 252
emission 127 nuclear fusion 253 nuclear fusion 253, 268, 269
from stars 265, 266 metals nuclear medicine 248–249
lenses 136, 140 transformers 209 nuclear power 15, 38, 245,
magnifying glass ray diagram magnetism 73, 74, 196 conduction 46, 153, 164
143 246, 251, 252
pinhole camera 129 see also electromagnetism Earth’s interior 255 nuclear reactors 252
redshift 265 magnets 196, 197 nuclear weapons 251
reflecting and absorbing 147 resistance 163, 164 nucleus
reflection 127, 130, 132 see also electromagnets microphones 115, 208
refraction 131, 133 magnification 143 microwaves 148 atomic models 239
refractive index 138–139 magnifying glasses 143 atomic structure 237
speed of 117, 127, 128, 138, magnitude Milky Way 263 nuclear fission 250–251
148 mirrors 128, 130 nuclear fusion 253
total internal reflection 133, scalars and vectors 66 models, scientific 16 radioactive decay 240, 241,
134–135, 139 stars 270, 271 moments 84–85
visible 145, 147, 148, 149, main-sequence stars 268, 271 momentum 66, 100–101 242–243
264 manometers 231
waves 113, 117, 127, 128, mantle, Earth’s 255 changing 104 OPR
129, 131, 265 elastic and inelastic collisions
Mars 258 ocean breezes 220
light bulbs 163, 185 102–103 Ohm’s law 161, 167, 169
light energy 41, 183 mass Moon 12, 94, 96, 260 ohmic conductors 169
light-dependent resistors (LDRs) ohmmeters 174
and acceleration 97, 98–99 eclipses 261 ohms 157
174, 176, 177 center of 86–87 moons 258, 259 oil 38, 40
lightning 117, 192–193 conservation of 212 motion opaque materials 127
lightning rods 182 and density 216, 217 optical fibers 134
limit of proportionality 80, 81 acceleration 68–69, 98–99 orange giants 270
line graphs 23 and gravitational field 94 braking distance and energy orbits 262
linear equations 28 inertial 97 oscilloscopes 115, 206, 207
linear relationships 24 kinetic and potential energy 108–109 ossicles 118
liquids 212, 213, 214 calculating speed 62 overheating 185
52–53 car safety features 107 oxygen 269
boiling 223, 224 circular 96 paper mills 247
density 216, 217 and momentum 100, 101 elastic and inelastic collisions parachutes 69, 106, 110,
evaporation 224
latent heat of vaporization 225 nuclear fusion 253 102–103 111
pressure 229 first law of 75 parallel circuits 155, 158–159,
seismic waves 123 stars 268 forces and 73, 96–111
loads 56 and weight 79 measuring speed 63 165, 166, 168
longitudinal waves 114, 115, mass number 238, 242, 243 momentum 100–101, 104 parallel plates 194
position–time graphs 64–65 particles
123, 128 massive stars 268–269 scalars and vectors 66
loudness 115 second law of 97 atoms 237
loudspeakers 114, 208 materials, refractive index 138–139 speed 61 and density 216
lubricants 59 mathematical models 16, 28–29 stopping distance 105–106 internal energy 218
luminous objects 127 matter terminal velocity 110–111 metals 46
lunar eclipses 261 third law of 92, 93 in motion 214
lunar phases 260 changes of state 213, 224 velocity 67 radioactive 241
dark 266 velocity–time graphs 70–71 states of matter 212
MN density 216–217 motor effect 202–203, 204, 208 waves 114
and expansion of the Universe motors pascals 227
machines 89 electric 204 peer review 11
levers 88–89 267 relays 201 pendulums 54
other simple 91 heat expansion 215 nearsightedness 141 percentages 29
scanning 121 heating curves 223 nebulas 264, 268, 269 period, wave 116
internal energy 218 PET (positron emission
maglev (magnetic levitation) latent heat calculations 225 Neptune 259
trains 201 and mass 79 tomography) scanning 248,
particles in motion 214 neutron stars 269 249
magnetic dip/inclination 198 plasma 191 photogates 63
magnetic fields 93, 197 specific heat capacity 219–222 neutrons 190, 237, 238, 241, photoresistors 174
states of 212–213 physical changes 213
Earth’s 198 temperature and changes of 242–243 pie charts 22
electric motors 204 pinhole camera 129
electromagnetic induction 205 state 224 nuclear fission 250, 251 pistons 235
electromagnets 199–201 waves 113, 114 pitch 115, 118
generators 206, 207 measurements 20 Newton, Isaac 13, 75, 92, 93, pivots 84, 88, 89
loudspeakers and microphones accuracy and precision 21, 26 planets 258–259
errors 26 94, 97 formation of 268
208 scalars and vectors 66 Newton’s second law 97 orbits 262
motor effect 202–203 SI units 30 Newton’s cradle 100
speed 61, 63 newtons 74
medicine night sky 12, 263, 271

background radiation 245 nitrogen 269

hazardous radiation 151, 246 noncontact forces 73, 93
nuclear 248–249
radioactive isotopes 247 nonionizing radiation 151

ultrasound scans 121 nonohmic conductors 169, 170
nonrenewable energy 38, 40
melting 213, 216, 223, 224 normal, the 131, 132, 137, 139
nuclear energy 34
Mercury 258 nuclear equations 242–243

286

planets continued radiation continued resistance continued shape
planetary motion 12, 13, thermal energy 42–45 calculations 167–168 deformations 83
258–259, 262 types of 241 current and voltage graphs
169–170 elastic and inelastic deformations
plastic, static electricity 188 radiators 48 light-dependent resistors 174 80, 81
plugs 180, 181, 182, 185 power in circuits 171
plum pudding atomic radio telescopes 13 thermistors 175 forces and 73, 82
radio waves 13, 63, 148, 150, in wires 162–164
model 239 inelastic collisions 103
151, 264 resistors 157
plumb line 87 current and voltage graphs 169 shells, electron (energy levels)
radioactivity light-dependent 174, 176, 177
Pluto 259 background radiation 245 in series and parallel circuits 149, 237, 239
half-life 244 165–166
polar orbits 262 hazards 246 thermistors 175, 176, 177 shielding, radiation 246
nuclear equations 242–243 variable 161 SI units 30
poles nuclear fission 250–251
nuclear fusion 253 resolving forces 78 sight see vision
Earth’s 198, 256, 257 nuclear medicine 248–249 resultant forces 76–77 significant figures 21
nuclear power 252 retina 136
magnetic 196, 197 radioactive decay 240, 241, ripple tanks 119, 124, 137 sine 78
risks, technological 15
positrons 241 242–243 rock 255 sine waves 54
rockets 57 sinking 230
potential difference see voltage radioactive isotopes 244, 248, rocky planets 259
potential dividers 176, 177 rotational forces 90 skydivers 110–111
potential energy 218 249 rounding 21
radioactive waste 38, 252 rubber, static electricity 188, 189 smoke alarms 247
power types of radiation 241 Russell, Henry 271 Snell’s law 138, 139
in circuits 171 using radioactive isotopes 247 Rutherford, Ernest 239 solar eclipses 261
and energy 56–57 solar energy 36
energy efficiency 59 radionuclide scanning 248 S solar system 11, 12, 258–259,
radiotherapy 248, 249
input and output 210 safety 262, 263
transmission 186 radon 245 cars 107
power ratings 183 rainbows 146 conducting experiments 17, 19 solenoids 199–200
power stations 37, 179 ramps 91 fuses and circuit breakers 181 solids 212, 213
carbon capture 40 random errors 26 preventing electric shocks 182
radioactive hazards 246 density 216, 217
coal-fired 245 ray boxes 132–133 speed and 109 heat expansion 215
generators 37, 207 latent heat of fusion 225
nuclear 38, 245, 246, 251, 252 ray diagrams 129, 132–133, safety cages 107
power transmission 186 Sankey diagrams 41 and light 127, 128
precision 26 142, 143, 144 satellites
predictions 10, 11, 25 reaction forces 73, 74, 76, 92 melting 223, 224, 225
reaction time 106 moons 259, 260
pressure real images 129, 142 orbits 262 seismic waves 123
atmospheric 228 rectification 170 Saturn 259
barometers and manometers scalar quantities 66, 67 speed of sound 120
231 red dwarfs 270 scale diagrams 77, 78 sonar 122
floating and sinking 230 red giants 268, 270 scans, ultrasound 121
in gases 232–235 scatter graphs 23 sonograms 121
in liquids 229 red supergiants 268 scientific method 10–11, 12 sound 114
surface 227 redshift 265 scientific models 16
and temperature 234 reflection 128, 129, 130, 132 scientific progress 12–13 compared with light 128
and volume 233 scientific theories 11 hearing 118
work and temperature 235 and absorption 147 scrapyards 200
screws 91 loudspeakers and microphones
primary waves (P-waves) 123 iridescence 125 seasons 256–257 208
principle of moments 85 secondary waves (S-waves) 123
prisms 145 law of 132 seismic waves 123, 255 oscilloscopes 115
selective breeding 14 sonar 122
proportional relationships 24 rainbows 146 semiconductors 175 speed of 117, 120, 128
total internal 133, 134–135, 139 sensor circuits 176–177 waves 35, 113, 114–115, 117,
protons 190, 237, 238, 239, series circuits 155, 156,
reflectors, infrared radiation 118, 120, 122, 128, 208
241, 242–243 43–45, 51 158–159, 165, 167
shadow zones 123 sound energy 183
Ptolemy 12 refraction 128, 129, 131, 133 shadows 127
pulleys 91 space
pulling 73, 74, 82, 83 converging and diverging lenses Big Bang or steady state 267
140 classifying stars 270–271
pump action 235 Earth’s structure 255
light and color 145–146 eclipses 261
pushing 73, 74, 83 refractive index 138–139 expanding Universe 266
waves and 137 galaxies 263
radar, speed guns 63 Moon 260
radiation 43–45 regular reflection 130 observing 264
relays 201 orbits 262
background 245 renewable energy 36–37, 40 redshift 265
cosmic microwave background seasons 256–257
representational models 16 solar system 258–259
267 star life cycles 268–269
electromagnetic 148–149, repulsion 93, 197
space telescopes 13, 264
151, 264, 265 electromagnetic induction 205
magnetism 196 sparking 192–193, 194
energy transfers 35, 50, 51 static electricity 188–189, 194
hazardous 151, 246 resistance 25, 156, 157 spatial models 16
radioactive decay 240 changing 161 specific heat capacity 219–222
in space 264, 271
current and voltage specific latent heat 225

spectroscopy 265
speed 61

287

speed continued Sun continued trigonometry 78 voltage continued
and acceleration 68–69 radiation from 39, 44 transformers 209–210
safety 17 trip switch 181
braking distance 108–109 seasons 256–257 voltmeters 157, 162
calculating 62, 65 solar system 11, 12, 258–259 troposphere 255 volume
speed of light 127
of light 117, 127, 128, 138, 148 tumors 249 and density 216, 217
measuring 63 supernovas 266, 269 and gas pressure 233
supersonic cars 106 turbines 34, 36, 37 measuring 20
orbits 262 surface pressure 227
position–time graphs 64–65 systematic errors 26 turning effect WX
of sound 117, 120, 128
TUV gears 90 wasted energy 41, 185, 186
and stopping distance 105 water
and velocity 67 tables 22 moments 84–85
of waves 117, 119, 137 tangents 65 twisting 83 density 216
speed guns 63 tectonic plates 255 ultrasound 118, 121, 122 latent heat of fusion 225
telescopes 12–13, 264 pressure 229
spiral galaxies 263 temperature ultraviolet 13, 149, 151, 264 reflection 135
unbalanced forces 75 refraction 137
split-ring commutator 204, 207 and changes of state 224 Universe refractive index 138
spring constant 80 heating curves 223 sound waves 122
springs 55, 80–82 insulators 47 Big Bang 265, 266, 267 waves in 113, 119
and internal energy 218 expanding 265, 266, 267 water resistance 74
squeezing 80–81 latent heat calculations 225 models of 12 water vapor 213, 224
stability, center of mass 86–87 lightning 191 scale of 263 watts 56, 171
standard form 29 and pressure in gases 232, 234 steady-state model 267 wave energy 37
specific heat capacity 219–222 understanding 13 waveforms 115
stars of stars 270, 271 upthrust 230 wavelength 113, 116–117, 119,
classifying 270–271 thermistors 175, 176, 177 uranium 240, 243, 250, 252
color and temperature 271 and work 235 120
formation of 269 tension 73, 83, 96 Uranus 259 reflection and absorption 147
galaxies 263 terminal velocity 110–111 vacuum flasks 51 waves 113
life cycles 13, 268–269 theories, scientific 11 vacuums, light in 127, 138 electromagnetic 13, 42,
light from 265 thermal conductors 46, 47 Van de Graaff generator 189
magnitude (brightness) 271 thermal energy 34, 35, 42–49, vaporization, latent heat of 225 148–149, 151
size 270 variables interference 124
55, 163, 218, 220 light 113, 117, 127, 128, 129,
states of matter 212 thermal equilibrium 42 dependent and independent 18
changes of state 213 thermal expansion 215 discrete and continuous 23 131, 265
density and 216 thermal images 43 patterns in data 24 longitudinal and transverse 114
latent heat calculations 225 thermals 48, 49 vector quantities 66, 67, 73, 100 radio 150
thermistors 175, 176, 177 velocity 61, 66, 67 and refraction 137
temperature and changes of thermometers 175, 215 acceleration and 68 seismic 123, 255
state 224 thermosphere 255 sonar 122
thinking distance 105, 106 and momentum 100, 101 sound 35, 113, 114–115, 117,
static electricity 153, 188–194 Thomson, J. J. 239
attraction by induction 190 thorium 240, 243 orbits 262 118, 120, 122, 128, 208
attraction and repulsion 188–189 thunder 191 terminal 110–111 speed of 117, 119
dangers of 192–193 tidal energy 14, 37 velocity–time graphs 70–71 ultrasound 121, 122
electric fields 194 tides 260 Venus 258 wave equations 116–117
uses of 191 timbre 115 weather forecasting 231
time vibration weight
steady-state model of the center of mass 86–87
Universe 267 measuring 20, 63 particles 46, 128, 215, 218 floating and sinking 230
position–time graphs 64–65 and mass 79
steam 213, 225, 252 velocity–time graphs 70–71 waves 113, 114, 118, 120, 208 wheels 91
stellar equilibrium 268 tissue virtual images 129, 130, 143, 144 white dwarfs 269, 270, 271
damage 151 visible light spectrum 145, 147, white light 145, 147
step-up/step-down transformers scanning 248–249 wind energy 36
trains 148, 149, 264 wires
186, 209 electric 173 earth 182
maglev 201 vision 127, 136 electrical wiring 180
sterilization 247 transducers 121 correcting 141 electromagnetic induction 205
stopping 104 transformers 186, 209–210 magnetic fields 199
stopping distance 105–106 translucent materials 127 voltage 154 motor effect 202
transparent materials 127, 147 calculating energy 172–173 resistance in 162–164
stopwatches 63 transverse waves 114, 115, 123, charge 160 work 55, 56, 80
and temperature 235
storm clouds 192 128, 148 current electricity 153 wrenches 84
X-rays 13, 15, 149, 151, 264
stratosphere 255 current and voltage calculations
167–168
street lights 174, 176
current and voltage graphs
stretching 55, 80–81, 83 169–170

sublimation 213 electrical circuits 154
electrical wiring 180
substations, electricity 186
electromagnetic induction 205
Sun
atmosphere 261 generators 206, 207
measuring 156, 157
distance from Earth 263 power in circuits 171
eclipses 261 power transmission 186

heliocentric model 12 resistance 161–166

light from 145 sensor circuits 176–177

nuclear fusion 253 series and parallel circuits
orbits around 262
158–159, 165–166

288

Acknowledgments

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