Module 5.3 - Gravitational Fields ✓

Question 1

What is a ‘force field’?

Answer 1

A force field is a region where an object will experience a non-contact force

Question 2

What is the equation for Newton’s law of gravitation?

Answer 2

F = -GMm/r^2

Question 3

In which way do gravitational field lines point?

Answer 3

In the direction a small test mass would move in the gravitational field

Question 4

Define gravitational field strength?

Answer 4

Gravitational field strength is the force per unit mass (also called the acceleration due to gravity)

Question 5

Is gravitational field strength scalar or vector?

Answer 5

Grav field strength is a vector that points towards the centre of the mass you’re looking at (it could be negative if you define the positive direction differently)

Question 6

Why do those gravity equations have random negatives in them?

Answer 6

r is the distance from the centre of a big mass M, so the positive direction is away from the mass. However attraction is towards the mass so F/g must be -ive

Question 7

Define gravitational potential

Answer 7

The gravitational potential at a point is the work done moving a unit mass from infinity to that point

Question 8

What is gravitational potential difference?

Answer 8

Gravitational potential difference is the difference in gravitational potential between two points in a gravitational field

Question 9

What is the equation for gpe that accounts for changes in g?

Answer 9

change in E = m * (change in Vg)

Question 10

What is escape velocity?

Answer 10

Escape velocity is the velocity needed by an object to have enough energy to escape a gravitational field

Question 11

What is the equation for escape velocity?

Answer 11

v = sqrt(2GM/r)

Question 12

Define a satellite?

Answer 12

A satellite is a small mass which orbits a much larger mass

Question 13

State kepler’s first law

Answer 13

Each planet moves in an ellipse around the Sun, with the sun at one focus

Question 14

State kepler’s second law

Answer 14

A line joining the sun to a planet will sweep out equal areas in equal time periods

Question 15

State kepler’s third law

Answer 15

The period of the orbit and mean distance between the sun and planet are in the relationship:
T^2 <=>< r^3

Question 16

How are atmospheric thickness and gravity linked?

Answer 16

The more mass a planet has the larger the force further form it’s centre is. This means it can stop more atmospheric particles from escaping into space creating a thicker atmosphere

Question 17

How do you derive kepler’s third law equation?

Answer 17

The time for one orbit from circular motion is T = 2πr/v

sub in v = sqrt(GM/r) and re-arrange

Question 18

What is a geostationary satellite?

Answer 18

A geostationary satellite is a satellite that always stays above the same point on the earth’s surface

Question 19

Where can geostationary satellites orbit?

Answer 19

Geostationary satellites can only orbit along the equator of the Earth (they match the angular speed of the earth to do so)

Question 20

What is the force distance graph for a point mass in a gravitational field?

Answer 20

F
│¦
│ \
│    - - - - -
└────── r