P5 - Gravity and Orbits

Question 1

What happens if an object is travelling in a circle?

Answer 1

• If an object is travelling in a circle, it is constantly changing direction.
• This means there must be a force acting on it.

Question 2

What is an orbit?

Answer 2

• An orbit is a balance between the forward motion of the object and a force pulling it inwards.
• This is called a centripetal force - it is directed towards the centre of the circle.

Question 3

Why does the Moon orbit the Earth?

Answer 3

Moon orbits the Earth because of the centripetal force produced by the gravitational force between each planet and the sun.

Question 4

Why do planets orbit the sun?

Answer 4

• The planets move around the sun in almost circular orbits.

* The centripetal forces that make this happen are provided by the gravitational force between each planet.

Question 5

Why do artificial satellites orbit the Earth?

Answer 5

• The centripetal force is provided by the Earth, and they have a strong pull into the Earth’s orbit.
• They keep accelerating towards the Earth, but their tangential motion ( at a right angle to the acceleration ) keeps them in an almost circular orbit.

Question 6

What is the correlation between mass and gravitational force size?

Answer 6

• The greater the mass, the greater the gravitational force, and the farther it can travel.

Question 7

What is the correlation between distance & gravitational pull?

Answer 7

• The closer you get to a planet/star the greater the gravitational pull.

Question 8

What force holds Moons, artificial satellites and space stations in orbit?

Answer 8

• Gravity

Question 9

What orbit do periodic comets have?

Answer 9

• Periodic comets orbit the sun.

* They have a highly elliptical ( elongated ) orbit.

Question 10

How do comets change speed?

Answer 10

• Periodic comets orbit the sun with an elliptical orbit.
• The orbits take them a long way from the sun, then back close again.• The closer the comet is to the sun the greater the gravitational force of attraction
• Comets travels much faster nearer to the sun, than it does in more distant parts of the orbit.