3.3 MAN-MADE SATELLITES

CHAPTER 3
GRAVITATION

3.3 MAN-MADE SATELLITES

TEXT BOOK : PAGE 103 - 110

SUE ROSE

LEARNING STANDARD

3.3.1 Describe how an orbit of a
satellite is maintained at a specific
height by setting the necessary
satellite’s velocity.

3.3.2 Communicate on geostationary
and non-geostationary satellites.

3.3.3 Conceptualize escape Velocity

The International Space
Station, ISS can be seen
from the Earth because of
its large size and orbits at a
height of 498 km.

MEASAT satellite is difficult
to be seen because of its
small size and orbits at a
height of 35,786 km.

Satellites move in orbits at
specific heights and suitable
linear speeds.

How do man-made satellites
help to improve human life?

ACTIVITY 1 Determine the linear speed of a satellite =
=
Figure below shows the orbit of a
satellite around the Earth. A satellite
moving in a circular orbit around the
Earth experiences centripetal force,
which is gravitational force.

• GM is constant.
• Linear speed, v depends on the radius of its orbit.
• If a satellite is at a height, h above the surface of

the Earth:

Radius of orbit, r = R + h (R = radius of the Earth)

Linear speed of the satellite, v

• What is the requirement so that a
man-made satellite can be launched
to keep orbiting at specific heights
around the Earth at radius orbit, r?

• The linear speed of the satellite is

6.37 x 106

• What will happen to the satellite if
the linear speed of satellite is less
than the required linear speed?

• The satellite will fall to a lower orbit
and continue to revolve towards the
Earth until it enters the atmosphere.

• The movement of the satellite at a
high linear speed against air
resistance will generate heat and
causes the satellite to burn.

ACTIVITY 2 To compare between geostationary and non geostationary satellites

GEOSTATIONARY SATELLITE

A satellite that moves around
the Earth at certain height. In
a special orbit named the
Geostationary Earth Orbit.

Moves around the Earth in the
same direction as the direction
of the Earth’s rotation on its
axis

Orbital period T = 24 hours, that
is the same as the period of
rotation of the Earth

Always above the same
geographical location

ACTIVITY 2 To compare between geostationary and non geostationary satellites

NON-GEOSTATIONARY SATELLITE

A satellite that moves around
the Earth at changing orbit
height. Normally in a lower
or higher orbit than the
Geostationary Earth Orbit.

Orbital period is shorter or
longer than 24 hours

Above different geographical
locations at different times



Difference Characteristics

GEOSTATIONARY SATELLITE NON-GEOSTATIONARY SATELLITE

• Direction of motion same as the Direction • Direction of motion need not be
direction of Earth rotation of motion the same as the direction of the
Earth rotation

• T = 24 hours Period, T • T is shorter of longer than 24
hours

• Above the same geographical Position • Above different geographical
location Function locations

• Communication satellite • Earth imaging GPS, weather
forecast

• MEASAT Example • TiungSAT, RazakSAT, Pipit, ISS

ACTIVITY 4 Escape Velocity

• What is the meaning of escape velocity?

Escape velocity, v is the minimum velocity
needed by an object on the surface of the
Earth to overcome the gravitational force
and escape to outer space.

• When the escape velocity is achieved?

When the minimum kinetic energy of an
object is able to overcome its gravitational
potential energy.

Derived the formula for Kinetic Energy Gravitational
escape velocity: potential
An object is at a distance r ½ mv2 energy
from the centre of the Earth.
Mass of object is m and mas -GMm
of the Earth is M. r

Minimum Kinetic enery +
Gravitational Potential energy = 0

½ mv2 + [- GMm] = 0
r

v2 = 2GM
r



State factors affecting the escape velocity, v

The mass of the Earth, M
Distance, r of the object from the centre of
the Earth.

Benefits and Implication of Escape Velocity
1. Why the Earth can maintain a layer of atmosphere around it?

High escape velocity of the Earth =
11 200 m/s
Molecules in the atmosphere move
at average linear speed of 500 m/s,
that is lower than the escape
velocity from the Earth.
So air molecules that are moving
randomly will not be able to escape
from the Earth into outer space.

2. Why commercial aircrafts cannot escape into outer space?

Commercial aircrafts can fly at
linear speed of 250 m/s
Fighter jets can achieve supersonic
linear speed of up to 2200 m/s.
Both their linear speeds are lower
than the escape velocity from the
Earth (11 200 m/s)

3. How can a rocket achieve escape velocity from the Earth and
send the spacecraft into outer space?

The launching of rockets requires
large quantities of fuel to produce
high thrust that enables the rocket
to achieve escape velocity of the
Earth.
Hence, it can send the spacecraft
into outer space.

ACTIVITY 5 To solve problems involving escape velocity

1. Calculate the value of escape velocity

The moon has low gravitational
acceleration compare to the Sun.

The moon has low
escape velocity compare
to the Sun because the
mass of the Moon is
smaller than the Sun.