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A-Level Physics > 9: Gravitational Fields > Flashcards

9: Gravitational Fields Flashcards

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1
Q

What is a force field?

A

A force field is a region in which a body experiences a non-contact force

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2
Q

What are the two types of gravitational field?

A

Uniform field - Same force everywhere
Radial field - force exerted depends on the position of the object

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3
Q

What does Newton’s law of gravitation show?

A

The magnitude of the gravitational force between two masses is directly proportional to the product of the masses, and is inversely proportional to the square of the distance between them (where distance is measured between the two centres of masses)

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4
Q

What is the equation for Newton’s law of gravitational force?

A

F = Gm1m2/r^2

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5
Q

What is G (gravitational constant)

A

6.67x10^-11

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6
Q

What is gravitational field strength?

A

The force per unit mass exerted by a gravitational field on an object

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7
Q

What is the gravitational field strength (g) like in a uniform field?

A

Constant

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8
Q

What is the gravitational field strength (g) like in a radial field?

A

Variable

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9
Q

What is the general equation for gravitational field strength, used for both radial and uniform fields?

A

g = F/m

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10
Q

What is the equation for gravitational field strength (g) in a radial field?

A

g = GM/r^2

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11
Q

What is gravitational potential (V)

A

The work done per unit mass when moving an object from infinity to that point

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12
Q

What is gravitational potential at infinity?

A

zero

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13
Q

What happens as an object moves from infinity to a point?

A

Energy is released as the gravitational potential energy is reduced, therefore gravitational potential is always negative

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14
Q

What is the equation for gravitational potential?

A

V = -GM/r (radial field only)

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15
Q

What is gravitational potential difference (ΔV)?

A

Energy needed to move a unit mass between two points

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16
Q

How can you work out work done using gravitational potential difference?

A

work done = mΔV

17
Q

How do you create an equipotential surface?

A

Joining points of equal potential together

18
Q

What is the potential like across an equipotential surface?

A

Constant everywhere

19
Q

What is the gravitational potential difference when moving along an equipotential surface?

A

Zero, so no work is done also

20
Q

What is the relationship between gravitational potential (V) and the distance between the centres of two objects (r)

A

Inversely proportional

21
Q

What is Kepler’s third law?

A

The square of an orbital period (T) is directly proportional to the cube of the radius

22
Q

What is the equation for Kepler’s third law?

A

T^2 = 4π^2/Gm x r^3

23
Q

What is the total energy of an orbiting satellite?

A

The sum of the kinetic energy and the potential energy.
It is constant.

24
Q

What is the escape velocity?

A

The minimum velocity an object must travel at in order to escape the gravitational field at the surface of a mass.
This is when kinetic energy = gravitational potential energy

25
Q

What is the equation to work out escape velocity?

A

v = √2GM/r

26
Q

What is a synchronous orbit?

A

where the orbital period of the satellite is equal to the rotational period of the object

27
Q

What is the orbit for a geostationary satellite like?

A

They follow a specific geosynchronous orbit, so their orbital period is 24 hours and they always stay above the same point on the earth (as they orbit the equator)

28
Q

What are some applications of geostationary satellites?

A

TV and radio signals

29
Q

What are the orbits of low-orbit satellites like?

A
  • They have lower orbits in comparison to geostationary satellites
  • They travel faster so their orbital periods are smaller
  • Therefore they require less powerful transmitters and can potentially orbit across the entire Earth’s surface
30
Q

What are the applications of low-orbit satellites?

A
  • monitoring weather
  • making scientific observations about places which are unreachable
  • military applications

A-Level Physics (17 decks)

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