Satellites, gravity and circular motion

Question 1

What does every object do?

Answer 1

Every object in the Universe attracts every other object.These forces of attraction are usually only significent when they are on an astronomical scale.

Question 2

Why are plantets in orbit?

Answer 2

Planets stay in orbit around the Sun because of gravitational attraction.

Question 3

What is centripetal force?

Answer 3

Any object moving in a circle needs a force of attraction towards the centre of the circle. This is called centripetal force.

Question 4

The larger the mass.

Answer 4

The greater the gravitational force.

Question 5

The further away an object is.

Answer 5

The smaller the gravitational force.

Question 6

What does gravitational force obey?

Answer 6

An inverse square law: force ∝ 1/force2.

Question 7

The orbit time for a planet closer to the Sun is less because:

Answer 7

• The planet travels a shorter distance.
• The planet travels faster because there is a greater gravitational force.

Question 8

How does a satellite move?

Answer 8

A satellite moves at a tangent and gravity makes it accelerate towards Earth.

Question 9

How does a comet travel when travelling around the Sun?

Answer 9

Comets travel very quickly when close to the sun and very slowly when they are far away.

Question 10

Where do polar satellites orbit?

Answer 10

Polar satellites orbit above the North and South pole just 100 km - 20 km above Earth.

Question 11

How long is a polar orbit?

Answer 11

Most polar satellites orbit take 90 minutes to orbit the earth.

Question 12

What can polar satellites see?

Answer 12

Polar orbit satellites can see the whole of the Earth’s surface as the Earth rotates beneath them.

Question 13

Uses of a polar satellite.

Answer 13

They are used for imaging the Earth - including short range weather forecasting.

Question 14

Where do geostationary satellites orbit?

Answer 14

A geostationary satellite orbits above the equator.

Question 15

How long is a geostatonary orbit?

Answer 15

The time for one orbit is 24 hours - this means it always appears to be in the same position above the equator.

Question 16

Use of a geostationary satellite.

Answer 16

Geostationary satellites are used for communications.

Question 17

The nearer a satellite is to the Earth’s surface.

Answer 17

The shorter it’s orbit time.

Question 18

What is the distance travelled by a satellite?

Answer 18

• 2πr
• where r is the height of the satellite above the centre of the Earth.
• time = distance/speed.
• If r is small and speed is larger then time will be small - this is a polar orbit.

Question 19

What are the requirements of a geostationary orbit?

Answer 19

• All geostationary satellites must be in the same orbit.
• They cannot be too close together as their signals would overlap due to diffraction.