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Physics Paper 2 (Content) > Gravitational Fields > Flashcards

Gravitational Fields Flashcards

1
Q

What is meant by a force field

A

An area in which an object experiences a non contact force

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2
Q

Describe the similarities between gravitational and electric fields

A
  • Forces both follow inverse square laws
  • Use field lines to be represented
  • Both have equipotential surfaces
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3
Q

Describe differences between gravitational and electric fields

A
  • For gravitational force exerted is always attractive
  • Where as electric field the force can be either repulsive or attractive

DO NOT SAY POSITIVE OR NEGATIVE

  • Electric force acts on charge, while gravitational force acts on a mass
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4
Q

Newtons law of gravitation

A

Magnitude of force between two objects

  • directly proportional to product of masses
  • inversely proportional to the square of distance between them (hence inverse square law)
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5
Q

Definition of gravitational field strength

A

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

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6
Q

Equation for gravitational field strength for radial and uniform fields (two diff ones)

A

g =F/m

g = GM/r^2

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7
Q

Definition of gravitational potential (V)

A

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

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8
Q

Describe why gravitational potential is always negative

A
  • Gravitational potential at infinity is zero
  • As the object moves from infinity to a point, energy is released
    (As the gravitational potential energy is reduces)
  • Therefore gravitational potential must always be negative (since reducing from 0)
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9
Q

Definition of gravitational potential difference

A

Energy needed to move a unit mass between two points

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10
Q

Describe why gravitational potential difference is useful

A
  • It can be used to find the work done when moving an object in a gravitational field between two points

Since it is energy needed = work done

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11
Q

What is known about equipotential surfaces

A

Potential on an equipotential surface is constant everywhere

  • Therefore no work is done when moving along an equipotential surface
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12
Q

Describe the graph for gravitational potential against radius

A

Within the negative quadrant for the y axis

A curve tending towards the x axis (sort of a reciprocal)

Where the curve starts is the radius of the graph

The gradient is -g

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13
Q

Describe the graph of gravitational field strength against radius

A

Inverse proportional graph shape

Area under points on graph is gravitational potential difference

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14
Q

Explain how you can work the derivation of Kepler’s 3rd law

A

Centripetal force = gravitational force
Rearrange for v
Velocity is rate of change of momentum
Sub into v and solve for T

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15
Q

What is the total energy of a satellite

A

Kinetic energy + potential energy (its constant)

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16
Q

What is meant be escape velocity

A

The minimum speed that will allow an object to escape a gravitational field with no further energy input

In which the object will not fall back into the gravitational field due to attraction

17
Q

At what point is escape velocity reached in terms of energy

A

Object reaches escape velocity when its kinetic energy has been transferred to gravitational potential energy

18
Q

Derive the equation for escape velocity

A

KE = GPE

0.5 x m x v^2 = GMm / r
Little m’s cancel and solve for v

v = root 2GM/r

19
Q

What can we infer about escape velocity for different objects from the equation

A

Escape velocity will be the same for all objects

It is independent of mass of the object

20
Q

What is a synchronous orbit

A

When an orbiting body has a time period equal to that of the body it is orbiting

And in the same direction of rotation as that body

21
Q

What is a geosynchronous orbit

A

A synchronous orbit that is directly above the equator

22
Q

Which direction is the Earths rotation

A

West to east

23
Q

What is the orbital time period of Earth

A

24 hours

24
Q

What are the key features of geostationary orbit

A
  • Equatorial orbit
  • Moves west to east
  • Period of 24 hours
25
Q

Explain one use of geostationary satellites

A
  • Telecommunication transmissions
  • Base station on Earth sends the TV signal up to the satellite where it is amplified and broadcast to ground for desire location
  • Satellite receiver dish on surface must point towards same point in the sky
26
Q

What is a low orbit

A
  • Altitude is closer to the Earths surface than other orbits example polar orbits

Which are orbits from north to south pole

27
Q

Why are low orbits useful

A

Can take high quality photographs of Earths surface for:

  • Weather
  • Military applications

Physics Paper 2 (Content) (8 decks)

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