Chapter 4: Gravitational Fields

Question 1

Where are gravitational fields made

Answer 1

In the space around all masses

This creates a force which acts on any object placed in that field

Question 2

Gravitational field strength

Answer 2

At a point is the gravitational force exerted per unit mass on an object placed at that point

Question 3

Direction of field lines

Answer 3

Towards mass

Question 4

Newton’s law of gravitation

Answer 4

Any two point masses attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation

Question 5

Describe the Earth’s gravitational field strength at its surface

Answer 5

Roughly uniform

Equal to the acceleration of free fall

Question 6

Orbital period

Answer 6

The time taken for one complete orbit

Question 7

Derive Kepler’s third law

Answer 7

1. Orbital speed (v) = 2pir/T (speed = dist./time)
2. Speed of circular motion^2 = GM/r found by equating centripetal and gravitational forces
3. Equate orbital and circular motion speed and rearrange

Question 8

Define geostationary orbit

Answer 8

A satellite is positioned so as it orbits, the Earth rotates below it at the same rate

Question 9

Where is a satellite in a geostationary orbit

Answer 9

It will orbit around the equator

It will remain above a fixed point on the Earth’s surface