DK SCIENCE LAB

BUZZER 149

The elastic band should HOW IT WORKS
be taut enough that it
doesn’t fall off. The buzzing sound is caused by something called aeroelastic
flutter. This happens when a flexible object is in fast-moving air,
8 Stretch the rubber band over the adhesive putty and the air makes it flex back and forth quickly. The rubber
lumps. Check the band isn’t twisted and its sides band flexes about 200 times a second, which is the same
are parallel to but not touching the lollipop stick. frequency as a bee’s wings and so makes a similar sound. You
can create an even louder sound from flutter by sandwiching a
The folded card blade of grass between the sides of your thumbs and blowing
creates a streamlined through the gap between them.
shape that keeps the
buzzer facing in one Whirling the buzzer in B BZ Z
direction as it flies. circles causes air to
rush quickly over the

rubber band.

B BZ Z B
BB
BZ Z
Z

Z

If your buzzer loses its buzz B B BZ Z
after a few minutes, loosen
the rubber band from the B
adhesive putty and try again.
Z

Z

B BZ Z B B

Z

Z

9 Open out the wings slightly.
Find an open space where
your buzzer won’t hit any REAL WORLD: SCIENCE
TACOMA NARROWS BRIDGE
objects or people and whirl it
In 1940, the world’s third-
around in large circular largest suspension bridge (the
Tacoma Narrows Bridge in the
movements as fast as you USA) was hit by strong winds
and began to flutter. It twisted
can. If the buzz is too back and forth with such
violence that it tore itself apart
quiet, experiment with and collapsed. Today, engineers
go to great lengths to prevent aeroelastic flutter in structures
thick and thin rubber As you whirl the affected by fast-moving air, such as aircraft and bridges.

bands until you find the buzzer, the string pulls
one that makes the taut. The pulling force
loudest buzz. is called centripetal
force and stops the
buzzer flying off in
a straight line.

The strings are
held in tension.

You can adjust how
tightly the strings are

held by turning the
hooks at the head.

GUITARSTRINGED INSTRUMENT VIBRATIONS

Making music can be a great way to explore the science of
sound – and this guitar can help you do both. With fishing line
for strings and an ice cream tub for a body, it’s easy to make.
And if you set it up right, it will make a surprisingly tuneful
sound. In fact, you’ll find this project really hits the right notes!

The vibrations of the
strings are passed on to
the body of the guitar.

The vibrating body
of the guitar disturbs
the air, sending out
sound waves into the
air around it.

152 LIGHT AND SOUND Time Difficulty
90 minutes Hard
GUITARHOW TO MAKE A

The two most important features of your guitar are the
strings and the body. In this project, the strings are made
of fishing line. The body of your guitar is made of a plastic
ice cream tub. The neck is made of corrugated cardboard.

WHAT YOU NEED

Scissors 45 cm (18 in)

Paint 1 Make pencil marks every 5 cm (2 in) down
the shorter side of the cardboard. Repeat
Paintbrush the marks in the middle.

Felt-tip pen
Duct
tape

Adhesive putty Large Glue
bulldog clip

Pencil

Ice cream tub
19 cm x 15 cm
(71⁄2 in x 6 in)

Medium-weight
fishing line

Corrugated cardboard Eight screw hooks
45 cm x 35 cm Ruler
(18 in x 14 in)

2 Using the ruler, draw straight lines that join
the marks you made and extend them across
the whole width of the cardboard.

GUITAR 153

3 Cut along the lines, so that you end up with 4 On one of the long rectangles, make a pencil
seven long rectangles of cardboard, each mark 221⁄2 cm (9 in) from one end – halfway
45 cm (18 in) long and 5 cm (2 in) wide. along its length.

Stacking and gluing
the pieces together
like this increases

the strength
of the neck.

5 Divide the long rectangle into two equal pieces, 6 Stick the other six long rectangles together
by cutting where you made the pencil mark. by applying glue between them and putting
them together into a stack.

8 Mix some glue into the paint.
This will thicken it and add
strength to the neck when
applied to it.

7 Now glue the two shorter pieces on top of one
end of the stack, so that the stack is thicker
at one end. This is the neck of the guitar.

154 LIGHT AND SOUND

The neck of a 9 Apply the glue-and-paint mixture all
guitar has to be over your guitar’s neck, and leave it for
strong enough to half an hour or so to dry and set.
withstand the
stress of the tight
strings against it.

To make it look like a real guitar, we’ve decorated
ours with painted frets. Frets are metal strips on
the neck that help the player find the notes.

This is to ensure
that the neck will

line up with the
side of the tub.

10 Apply a few pieces of duct tape 11 Stand the tub on one of its shorter sides.
around both ends of the guitar’s Hold the thick end of the neck against the
neck, to strengthen them further. rim of the tub. Make a mark on the tub next to the
thinner part of the neck.

Try to position
the neck in the
middle of the
tub’s side.

12 Hold the thin end of the neck against the Put adhesive
end of the tub, and line up the top of it putty under the
with the mark you made. Draw around the neck.
tub to protect
the table.

13 Repeat steps 11 and 12 at the other end
of the tub. Now carefully use the scissors
to make a hole in the middle of each rectangle,
from the inside of the box outwards.

GUITAR 155

Take care as
the edges of the
pieces will
be sharp.

14 Neatly cut out each rectangle, starting at If the neck doesn’t fit,
the hole you made. Cut straight lines out to you might need to make
the corners first, then along the rectangle’s sides. the hole a bit bigger.

15 Push the thin end of the neck through the
two holes, until the thick part of the neck
juts up against the side of the tub.

Make two of the
holes closer to
the end than the
other two.

16 Line up a ruler at the thick end of the 17 Screw the four hooks into each of the
neck. Mark dots at 1 cm (1⁄2 in) intervals, holes. These will hold the guitar’s strings.
making two of them closer to the end, as shown.
19 Screw a hook into each
of the four dots you
drew. In each case, make sure
the open part of the hook
faces away from the body
of the guitar.

18 Draw four more dots on the tape at the
thin end of the neck. Make these
1 cm (1⁄2 in) apart, too, but all in a line this time.

156 LIGHT AND SOUND

Make sure the
strings don't

cross or touch
one another.

20 Cut four pieces of fishing line, 10 cm 21 At the thick end of the neck, attach
(4 in) longer than the distance from each length of fishing line to a hook.
one set of hooks to the other set of hooks. Tie a double knot as tightly as you can.

23 Pull the ends of the four lengths of fishing
line together, keeping them taut, and then
secure them with the bulldog clip. See what happens
when you move your fingers up and down the guitar
neck while plucking the strings at the same time.

22 Pull the free end of each length taut and Pluck one or more strings
wrap it once or twice around a hook at with the thumb or fingers
the other end. Do not tie the line at this end. of your other hand.

Press down on one or The body of the
more strings with the guitar is what
fingers of one hand. amplifies the sound.

Tighten the strings There should be You can trim the
by turning the a gap between the ends of the strings,
hooks at this end strings and the rim
until they are taut. of the tub. but don’t make
them too short.

HOW IT WORKS GUITAR 157

Plucking a string on your guitar causes the string to vibrate many times Plucking the string
per second. The more tension there is in the string (the more tightly it’s causes it to vibrate.
pulled), the more rapidly it vibrates – and the higher the pitch. Pressing
a string also raises the pitch. When you press a string, it touches the
guitar body in the middle and only its lower half vibrates. This produces
a note one octave higher. The strings cause the body of the guitar to
vibrate, which disturbs much more air, because it has a larger surface
area. This amplifies the vibration of the strings, making it louder.

Pressing the strings down with your The length, tension, Without the body of
fingers on the cardboard changes and thickness of the the guitar, the sound

the length of the string, which string all affect waves created by
changes the note. the note produced. the string’s

As the body of the vibrations would
guitar vibrates, it barely be audible.
amplifies the sound

of the strings.

REAL WORLD: TECHNOLOGY
ACOUSTIC GUITAR

Acoustic guitars have six strings, with each one being a different thickness.
The thicker the string, the lower the note it makes. This allows a guitar to
produce a great range of notes and sound. Also, unlike your ice-cream-tub
guitar, acoustic guitars have a closed front part, with a sound hole, which
helps to amplify deeper sounds, as the air inside the guitar is
compressed and expands. Finally, the material the guitar is made
from greatly affects the sound, as certain materials produce
different kinds of sound. Though wood is the most common
material, acoustic guitars can also be made from metal or plastic.

158 REFERENCE

GLOSSARY

ACID CAM CRANK FLUTTER

A substance that has a pH of A machine part that turns A machine part that can turn An energetic vibration created
less than 7. Strong acids (with rotation into back-and-forth rotation into to-and-fro motion as an object moves through the
pH between 1 and 3) can burn or up-and-down motion. or do the opposite. air (or as air moves past it).
your skin. Weak acids (with pH The forces exerted by the air
between 4 and 7) are present CARBON DIOXIDE CYLINDER cause the object to turn one
in vinegar, lemon juice, and cola. way, then the other.
A chemical compound that A three-dimensional shape that
AERODYNAMICS is found as a gas in the has a circle as its cross-section. FORCE
atmosphere and in fizzy drinks.
The study of how air moves DENSITY A push or a pull. Forces change
around objects, and how the CHEMICAL how an object moves: by causing
air produces forces such A measure of how much it to start or stop moving, speed
as air resistance and lift. A substance that is the same mass is present in a certain up or slow down, or change
all the way through – it is not volume of a substance. direction. Forces can also
AIR RESISTANCE a mixture. Chemicals can be change the shape of an object.
elements or compounds, and ELECTRON
A force that slows down may be liquids, solids, or gases. FRICTION
moving objects as they A negatively charged
travel through air. CHEMICAL REACTION particle found in atoms. A force between surfaces that
Electricity is a flow of electrons. are in contact. Friction between
ATMOSPHERIC A process in which the atoms of a tyre and the ground pushes a
PRESSURE two or more chemicals interact ELEMENT bicycle along as the wheels turn.
to make new chemicals.
The pressure of the air around A substance made of just one GEL
you, also known as air pressure. COMPOUND type of atom that cannot be
broken down into a simpler A mixture in which tiny drops
ATOM A chemical made of two substance by chemical reactions. of liquid are held in a solid. Jelly
or more elements. Water is a gel. A gelling agent is a
A tiny particle of matter. An is a compound made of the ELLIPSE substance that is added to
atom is the smallest part of elements hydrogen and oxygen. water to turn it into a gel.
an element that can exist. An oval, or flattened circle.
COMPRESSION The orbits of planets around GENERATOR
BASE the Sun are elliptical.
A squashing force, the opposite A device that produces
A substance that has a pH of tension. ENERGY electricity when it spins around.
of more than 7. A base is the
chemical opposite of an acid. CONDUCTION The ability to make things GRAVITY
happen. Energy can take various
BEARING The flow of heat or electricity forms, such as electrical energy, A force that pulls objects
through a material. kinetic energy (the energy of together. Earth’s gravity pulls
Part of a machine that reduces moving objects), and potential things towards the ground.
friction between moving parts. CONDUCTOR energy (stored energy).
There are bearings in wheels,
for example, that allow the A material through which EVAPORATION
wheel to spin freely. heat or electricity flows easily.
Metals are good conductors. The process by which a liquid

turns into a gas.

GLOSSARY 159

HYDROGEN ION MIXTURE RADIATION VIBRATION

A hydrogen atom that has A substance made of two or The loss of heat from a hot A very rapid back-and-forth
either lost or gained an electron. more compounds or elements. object (as it gives out infrared movement. Guitar strings
The more hydrogen ions in a A mixture can be composed radiation). Also short for vibrate when you pluck them,
solution, the lower the solution’s of solids, liquids, and gases. electromagnetic radiation. creating sound waves.
pH. Acids release lots of Air is a mixture of gases. Light, infrared, ultraviolet, radio
hydrogen ions when they dissolve waves, and X-rays are all forms VOLUME
in water, and bases gain them. MOLECULE of electromagnetic radiation.
The amount of space something
INSULATOR Two or more atoms RECYCLING takes up, normally measured in
joined together. millilitres, litres, or cubic metres.
A material through which The process of reusing
heat passes slowly. Your ORBIT something that is no WAVELENGTH
clothes insulate you, slowing longer needed.
down the loss of your body The path of a planet, comet The distance between two peaks
heat to the air around you. or asteroid, around the Sun – SOLUTION of a wave. In a sound wave,
or the path of a moon or a the wavelength is the distance
ION satellite around a planet. The A mixture where one substance between one point of highest
force of gravity keeps objects is dissolved in a liquid. air pressure and the next.
An atom that has a negative in their orbits.
or positive electric charge. SOUND WAVE WEIGHT
pH
LEVER An invisible wave that travels The downward force on
A measure of the concentration through air (or through liquids an object caused by gravity.
A rigid bar that modifies force of hydrogen ions in a solution. and solids) as alternating zones The more mass something
or motion when it swings around The more hydrogen ions, the of high and low pressure. has, the more it weighs.
a fixed point known as a pivot. lower the pH, and the more
acidic the solution. SPECTRUM
LIFT
PIGMENT A spread of colours produced by
An upward force on an object splitting light into the colours of
moving through the air. It is the A colourful substance. which it is made, as happens in
result of the air pressure being Inks, paints, and flowers a rainbow.
greater beneath the object than all contain pigments.
it is above. TENSION
PRESSURE
MASS A pulling force, the opposite
A measure of how much a force of compression.
A measure of the amount pushes on a surface.
of matter (stuff) in an object. TURBINE
The force of gravity pulls PYRAMID
on everything with mass, A device with rotating fan blades
so the more mass something A three-dimensional shape with that are driven by the pressure
has, the more it weighs. a point at the top and a triangle of gases, liquids, or steam.
or a square at the base. Turbines powered by the wind
or by moving water are often
used to generate electricity.

160

INDEX submarines 23
A chlorine 85, 87 gravity 24–29 P suspension bridges
columns 97 greenhouses 106
acids 78–81, 84–85 compounds 84, 85, 87 guitars 150–157 pantographs 112–117 98–105, 149
aeroelastic flutter 149 compression 97, 98, 105 parallelograms 91, 93,
air conduction 69 HIJ TU
construction science 115, 117
disturbances 142–145, heat loss 62–65, 69 pendulums 24–29 temperatures 62, 65, 69
151, 157 90–93 heat transfer 66–69 pH indicators 78–80 tension 29, 104, 150,
fast-moving 149 contact lenses 77 hydrogen 85 pitch 142, 157
insulation 65, 69 copper 82–87 infrared radiation 68, 69 polymers 77 156, 157
molecules 141 cranks 45, 48, 49, 55, insulation 62–65, 69 pontoon bridges 22 thermos 66–69
air fresheners 74–77 iron 86 potential energy 10–17 toilet flush 73
air resistance 17 58, 59 jibs 42, 43, 44–49 preservatives 77 torque 48, 49
airflow 38–41 cubes 91, 92 pressure 70, 73, 111 tower cranes 42–49
amplitude 131 cylinders 59, 94–97 KL pyramids 92, 93 towers 90–93, 98–105
artificial light 137 traction 17
atoms 85 DE kinetic energy 16, 17, R transferred energy 11, 16,
automatons 50–59 36, 37
daylight 137 radiation 69 30–37, 126–131
B density 23, 80, 81, 97 levers 116 reaction forces 41 triangles 90, 92–93, 106,
drawings, scaling up/down levitation 38–41 reeds 145
balanced forces 18, 23, lifting 42, 48–49 reflection 68, 69, 137 109–111
97, 104 112–117 light, splitting 132–137 reinforcement 119–123 umbrellas 117
ears 141 Lissajous curves 29 resistance 17, 123 upthrust 18, 19, 23
bases 78–81 electric cars 17 loads 19, 20, 22, 36, 42, rotation 36, 59
batteries 17 electrical energy 31, 37 VW
blades 30, 31, 32, 34–37 elements 137 48–49, 104, 122–123 S
blubber 65 ellipses 25, 28, 29 vacuums 69
bones, hollow 97 energy MO sails 41 vibrations 138–141,
buckminsterfullerine 111 salt 77, 85, 86, 87
building materials 118–123 potential 10–17 mainsprings 10, 11, 12, sandcastles 118–123 142–145, 150–157
buoyancy 18, 19, 22, 23 transferring 11, 16, 14–17 satellites 29 water, displacement 23
buzzers 146–149 30–37, 126–131 siphons 70–73 wavelength 131
engines, car 59 mass 16, 18, 22, 23, 93 slope stabilization 123 waves
C essential oils 74–77 matter 61, 97, 137 sodium 85, 87
evaporation 74, 77 mechanical linkages 117 sound 138–157 light 126–131
cables 98–99, 104–105 molecules 77, 97, 141 span 105 sound 138–141, 145,
cakes, baking 81 FG motion and airflow 38–41 spectrum, colour 132–137 146, 151
cams 50, 59 oil 62–65 speed 16, 17, 131 wind turbines 30–37
carbon 111 fats 64, 65 orbits 29 squares 91, 93 wind-up mechanisms
carbon dioxide 80, 81 fibre optic cables 131 osteons 97 stability 93, 96, 111, 123 10–17
cars 10–17, 59 floating 18–23 oxides 85, 87 stars 137 windsurfing 41
centre of gravity 93 frequency 131, 149 oxygen 77, 85, 87 steel 86 wings 148, 149
centripetal force 149 friction 16, 17, 28, 48, 123 stethoscopes 141
chemical reactions 78–81, gels 74–77 stress 111, 154
generators 37
82-87 geodesic domes 106–111

ACKNOWLEDGMENTS The publisher would like to thank the following for their kind Taylor (cb); Dreamstime.com: Horseman 82 (clb); Science Photo
permission to reproduce their photographs: Library: Steve Lowry (crb). 105 123RF.com: Songquan Deng (crb);
The publisher would like to thank the following people for their (Key: a-above, b-below/bottom, c-centre, f-far, l-left, r-right, t-top). Dreamstime.com: Ian Klein (clb). 111 Science Photo Library: Laguna
assistance in the preparation of this book: 17 Dreamstime.com: Masezdromaderi (tr); Getty Images: Stringer Design (bl). 117 Dreamstime.com: Hayati Kayhan (br). 123 The
Sam Atkinson and Pauline Savage for editorial assistance; Smiljka / Bill Pugliano / Getty Images News (cr). 23 Getty Images: Jeff Reinforced Earth Company: (br). 131 Dreamstime.com:
Surla for design assistance; Steve Crozier and Adam Brackenbury for Rotman / The Image Bank (bl). 29 iStockphoto.com: BlackJack3D STRINGERimages (cra). 137 NASA: ESA / Hubble & NASA (bl). 141
picture retouching; Pankaj Sharma, Ashok Kumar, Nityanand Kumar, (crb). 37 Dreamstime.com: Toldiu74 (bl). 41 Alamy Stock Photo: Getty Images: Inti St Clair / Blend Images (bl). 145 Dreamstime.
and Jagtar Singh for repro work; Sean T. Ross for testing the Michele and Tom Grimm (crb). 49 Dreamstime.com: Andrey Shupilo com: Elitsa Lambova (br). 149 Rex by Shutterstock: AP (bc). 157
experiments; Clarisse Hassan for additional illustrations; Helen Peters (br). 59 Dreamstime.com: Vladislav Kochelaevskiy (br). 65 Dreamstime.com: Mrchan (br).
for indexing; Victoria Pyke for proofreading; Emmie-Mae Avery, Amelia iStockphoto.com: oversnap (bl). 69 Depositphotos Inc: alexlmx (br).
Collins, Lex Hebblethwaite, Mollie Penfold, Melissa Sinclair, Kelly Wray, 77 Dorling Kindersley: Stephen Oliver (crb). 81 Dreamstime.com: All other images © Dorling Kindersley.
Abi Wright for hand modelling. Andrey Armyagov (bl). 93 Dreamstime.com: Jarrun Klinmontha (crb). For further information see: www.dkimages.com
97 Dorling Kindersley: Natural History Museum, London / Harry