Satellites, Gravity and Circular Motion

Question 1

When is a force of attraction significant?

Answer 1

When it’s on an astronomical scale.

Question 2

What does every object moving in a circle need?

Answer 2

Centripetal force, a force towards the centre of the circle.

Question 3

Why do planets stay in orbit around the Sun?

Answer 3

Gravitational attraction.

Question 4

What are the laws of gravitational force?

Answer 4

• The larger the mass, the greater the gravitational force
• The further away an object is, the less gravitational force it has
• Force ~ 1/distance^2

Question 5

Why do planets closer to the Sun have a smaller orbit period?

Answer 5

• The planet travels a shorter distance

- The planet travels faster because there is a greater gravitational force which acts as the centripetal force

Question 6

Which direction does a satellite travel in?

Answer 6

The tangent and gravity makes it accelerate towards Earth, causing it to orbit.

Question 7

What are the features of polar orbit satellites?

Answer 7

• Orbit above North and South poles just 100-200km above the earth
• Take about 90 minutes to orbit the Earth because time = (2Pi X r)/speed
• See the whole of the Earth’s surface as it rotates beneath them
• Used for imaging the Earth such as short-range weather forecasting

Question 8

What are the features of geostationary satellites?

Answer 8

• Orbits above the equator
• Orbit period is 24 hours meaning it stays in the same spot above the earth
• Used for communications
• Nearer to the Earth means a shorter orbit time
• All geostationary satellites must be in the same orbit but they can’t be too close together because their signals would overlap due to diffraction