Chapter 4 - Gravitational Fields

Question 0

Give one property that is always true for a gravitational field

Answer 0

It is attractive

Question 1

What is gravitational field strength?

Answer 1

The force on a unit mass when it is put in a gravitational field- (g=F/m)

Question 2

What is a gravitational field?

Answer 2

A force field around a mass

Question 3

Two bodies near each other will do what?

Answer 3

Exert equal and opposite forces on each other

Question 4

What is the weight of an object?

Answer 4

The force of gravity acting on the object giving it it’s mass

Question 5

What is a radial field?

Answer 5

A field in which the field limes are straight and converge towards a central point (the centre of a circle)

Question 6

What is a uniform field?

Answer 6

A region where the field strength is the same magnitude at every point in the field

Question 7

Describe the field lines in a uniform field

Answer 7

Parallel and equally spaced

Question 8

Describe how the magnitude of ‘g’ changes in a radial field

Answer 8

‘g’ decreases when the distance from the massive body increases

Question 9

What is the unit of gravitational field strength?

Answer 9

Nkg^-1

Question 10

What is gravitational potential?

Answer 10

The work done per unit mass to move a small mass from infinity to a point

(V=W/m)

Question 11

What happens to your gravitational potential as you move away from the Earth?

Answer 11

Your gravitational potential energy (GPE) increases

Question 12

What is your gravitational potential when you are in deep space?

Answer 12

Zero - provided that there a no large masses nearby

Question 13

What is the unit of gravitational potential?

Answer 13

Jkg^-1

Question 14

What are equipotentials?

Answer 14

Lines of constant potential around a point mass

Question 15

What happens to the gravitational field of the Earth as you move away from it?

Answer 15

The gravitational field becomes weaker

Question 16

What happens to the spacing between the equipotential lines as you move away from the Earth?

Answer 16

They become more spaced out

Question 17

What does it mean if field lines are concentrated in a small area?

Answer 17

It means that the field strength is strong - field strength is strongest when field lines are closest

Question 18

What is the potential gradient of a gravitational field?

Answer 18

Change in potential per unit distance

Potential Gradient= change in V/change in r

Question 19

How are gravitational field strength and the potential gradient linked?

Answer 19

‘g’ is the negative of the potential gradient

g=-V/r

Question 20

State Newton’s law of gravitation

Answer 20

The gravitational force between two point objects is proportional to the product of the two masses and inversely proportional to the square of the distance between them

Question 21

Which direction do the field lines around a spherical mass act?

Answer 21

Towards the centre of the sphere

Question 22

Why is the gravitational field strength zero at the centre of a spherical mass?
Inside the sphere, as r becomes smaller, less mass contributes. Only the mass within the radius will contribute to the field strength. At the centre, the mass which contributes to g is zero. As g=GM/r^2, if M=0 then g=0.

Answer 22

Inside the sphere, as r becomes smaller, less mass contributes . Only the mass within the radius will contribute to the field strength. At the centre, the mass which contributes to ‘g’ is zero

As ‘g’=GM/r^2 If M=0 then g=0

Question 23

What is the formula for gravitational potential around a spherical mass?

Answer 23

V=-GM/r

Question 24

Where does a geostationary satellite orbit, in respect to the Earth?

Answer 24

It orbits directly above the equator

Question 25

What is the time period of a geostationary satellite?

Answer 25

24 hrs

Question 26

What is a satellite?

Answer 26

A small mass which orbits a larger mass

Question 27

What provides the centripetal force for an orbiting satellite?

Answer 27

Gravitational Attraction (Gravitational Force)

Question 28

What are geostationary satellites used for?

Answer 28

Communications

Question 29

What is polar orbit?

Answer 29

Low Earth orbit around the poles of the Earth

Question 30

Why are weather satellites situated in polar orbits?

Answer 30

Polar orbits are closer to the Earth so the satellite will have a shorter time period than the Earth. As it orbits the Earth several times in one day, it can track weather patterns over a wide area.

Question 31

Why are geostationary satellites not suited for tracking weather conditions?

Answer 31

They are too far away from the Earth. As they have the same time period as the Earth, they are continually above the same point of the Earth - this means they can only track a limited area, not a broad area.

Question 32

What is the time period of a polar orbit?

Answer 32

Between 1.5-3 hrs