Gravitational Fields

Question 1

What does Newton’s Law of Gravitation state?

Answer 1

• that force (between two masses) is:
• directly proportional to the product of the masses
• inversely proportional to the separation of the centres squared
• always attractive

Question 2

Define a force field

Answer 2

a region in which a body experiences a non-contact force

Question 3

What type of quantity is a force field?

Answer 3

a vector quantity

Question 4

What does the gradient of a force-mass graph tell us?

Answer 4

the gravitational field strength

Question 5

Define a gravitational force field

Answer 5

a region in which an object with mass experiences weight

Question 6

Define gravitational field strength

Answer 6

the force per kg acting on a small test mass at a point in a gravitational field

Question 7

Define gravitational potential

Answer 7

the work done per kg in bringing a small test mass from infinity to that point in the gravitational field

Question 8

Why are GPE and gravitational potential always negatve?

Answer 8

• because gravity causes an attractive force

Question 9

For a radial field, what happens to the equipotential lines as r (radius) increases?

Answer 9

the spacing between equipotential lines increases

Question 10

What does the gradient of a V against r graph represent?

Answer 10

gravitational field strength (can be seen by formula sheet)

Question 11

Define escape velocity

Answer 11

the minimum speed an unpowered object needs in order the leave the gravitational field of a planet (or star)

Question 12

Where does a polar orbit go?

Answer 12

passes over both poles

Question 13

Are polar orbits high Earth orbits or low Earth orbits?

Answer 13

LEO (Low Earth Orbits)

Question 14

What is the 2 main advantages of a polar orbit?

Answer 14

• with a polar orbit, a satellite can cover the whole Earth as the Earth rotates
• also have short time periods, around 1.5 hours

Question 15

Give 3 uses of polar orbits

Answer 15

• mapping
• weather
• reconnaissance (spying)

Question 16

What is a geostationary orbit, list 3 things?

Answer 16

• an orbit above the equator
• same time period of the Earth
• stays above the same point on the Earth

Question 17

What are geostationary orbits used for?

Answer 17

communications

Question 18

What is a disadvantage of geostationary orbits?

Answer 18

they cannot see the poles (only see up to 20° above the equator)

Question 19

What is required for an object to escape from a gravitational field (in terms of energy)?

Answer 19

KE has to be sufficient to increase GPE to at least 0