3.7.2 - Gravitational Fields

Question 1

What is gravity?

Answer 1

Universal attractive force between all matter.

Question 2

What are gravitational fields?

Answer 2

A region of space which any mass will experience a force of attraction.

Question 3

What is the gravitational field strength?

Answer 3

The force per unit mass on a small test mass placed in the field.

Question 4

What indicates the strength of a field?

Answer 4

The separation of the field lines.

Question 5

What does the law of gravitation show about the relationship between field strength and radius?

Answer 5

F is proportional to 1/r^2

Question 6

What is gravitational field strength, g, measured in?

Answer 6

Nkg^-1

Question 7

What is gravitational potential?

Answer 7

The GPE that a unit mass at that point would have.

Question 8

When does gravitational potential = 0?

Answer 8

At infinity.

Question 9

When is gravitational potential negative?

Answer 9

On the surface of the mass. It increases with distance from the mass.

Question 10

What is gravitational potential, V, measured in?

Answer 10

Jkg^-1

Question 11

Under what graph is V?

Answer 11

A g r graph.

Question 12

What does Ep =

Answer 12

-GMm / r

Question 13

What does Ek =

Answer 13

GMm / 2r

Question 14

What does total energy =

Answer 14

-GMm / 2r

Question 15

What are equipotentials?

Answer 15

Lines which connect points of the same gravitational potential.

Question 16

How does work done change as you go across an equipotential?

Answer 16

It doesn’t - no work is done.

Question 17

What is a potential gradient?

Answer 17

The change in potential in a gravitational field per metre (V/r)

Question 18

What force keeps satellites in orbit?

Answer 18

Centripetal force.

Question 19

What is the relationship between the radius of a orbit and the time period?

Answer 19

T squared is proportional to r cubed.

Question 20

In an elliptical orbit what happens to the speed as the radius decreases?

Answer 20

The speed increases as does the KE. The GPE decreases.

Question 21

What remains constant in orbits?

Answer 21

The total energy (GPE + KE)

Question 22

What is the escape velocity?

Answer 22

The minimum velocity required for an object to escape from the planet when fired vertically from the surface.

Question 23

What does escape velocity =

Answer 23

root (2GM/r)

Question 24

What is a synchronous orbit?

Answer 24

When an orbiting object has an orbital period equal to the rotational period of the object it is orbiting.

Question 25

What is an example of geostationary satellite an example of?

Answer 25

Synchronous orbit as they are always in the same place above earth.

Question 26

Where are geostationary satellites positioned?

Answer 26

Above the equator.

Question 27

What are geostationary satellites used for and why?

Answer 27

Used for sending TV and telephone signals as the satellite is stationary relative to earth’s position, so you don’t have to alter the angle of your receiver to keep up with the position of the satellite.

Question 28

What are low orbiting satellites used for any why?

Answer 28

Used for communication as they are cheaper to launch and require less powerful transmitters as they are closer,. Also used for mapping, monitoring and the weather.

Question 29

Why are low orbiting satellites used for mapping?

Answer 29

As they are positioned in the plane of the north and south poles and because they rotate at a different angular speed to the earth, the satellite doesn’t stay over the same part of the earth and so the whole surface can be scanned.