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AQA A-level Physics > Section 7.1 Gravitational Fields > Flashcards

Section 7.1 Gravitational Fields Flashcards

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1
Q

What is a test mass?

A

A mass that has a negligible affect on the field

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2
Q

Define gravitational field strength

A

The force per unit mass

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3
Q

Show how acceleration is equal to the gravitation field strength when a mass is in free fall

A

a = F/m
a = gm/m
a = g

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4
Q

What is the unit of g?

A

N/kg

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5
Q

What does gravity affect?

A

Masses

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6
Q

What is a field line?

A

The path that a mass would take when placed in a gravitational field

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7
Q

What is a uniform field?

A

A field where the field strength is constant

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8
Q

What is a radial field?

A

Field strength is proportional to 1/r²

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9
Q

What is gravitational potential energy?

A

The work done moving a mass from infinity to a distance r away from the centre of the field

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10
Q

Why is gravitational potential energy negative?

A

because the potential energy at infinity is 0

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11
Q

What is gravitational potential?

A

The work done moving a mass from infinity to a distance r away from the centre of the field

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12
Q

What is an equipotential?

A

A surface of constant potential

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13
Q

True or false equipotentials are at right angles to field lines?

A

True

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14
Q

What is the eqaution for force in a radial field?

A

F = -G.M.m/r²

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15
Q

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

A

g = -G.M/r²

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16
Q

What is the equation for work done in a radial field?

A

W= -G.M.m/r

17
Q

What is the formula for gravitational potential?

A

V = -G.m/r

18
Q

What is the relationship between Force and work done?

A

Work done is the area under a force vs r graph

19
Q

What is the relationship between gravitational field strength and gravitational potential?

A

Potential is the area under a field strength vs r graph

20
Q

What is Keplers 3rd law?

A
  • T² α r³
  • square of the orbital period is directly proportional to the cube of the radius
21
Q

What is the formula for orbital velocity?

A

v= √G.M/r

22
Q

How is formula for orbital velocity derrived?

A

By equating force in radial field to centripetal force

23
Q

What is the formula that shows the formula for keplers 3rd law

A

T² =(4π/G.M).r³

24
Q

What is newtons law of gravitation?

A
  • Gravity acts on any objects which have mass and is always attractive.
  • force between two masses is directly proportional to the product of the masses
  • inversely proportional to the square of the distance between them
  • Modelled on point masses
25
Q

How is the formula for keplers 3rd law derived?

A

Equating force ina radial field and centripetal force

26
Q

What is the eqaution for escape velocity?

A

v = √ 2GM/r

27
Q

What is escape velocity?

A

the minimum velocity it must travel at, in order to escape the gravitational field at the surface of a mass

28
Q

How is the formula for escape velocity derrived?

A

Equating work done formula in a radial field and kinetic energy

29
Q

What is the total energy of a satelite?

A

Total energy of a satellite = kinetic energy + potential energy

30
Q

What is the formula for total energy of a satelite?

A

E = -GMm/2r

31
Q

What is a synchronous orbit?

A

the orbital period of the satellite is equal to the rotational
period of the object that it is orbiting,

32
Q

What is geostationary satellite?

A

they always stay above the same point on the Earth

33
Q

features of a geostationary satelelite?

A

Orbital period matches Earth’s rotational period exactly
 Satellite maintains same position relative to Earth
 Only one particular orbit radius is possible
 Travels west to east above Equator (in same direction as Earth’s
rotation)
 Orbit height is greater than polar orbit satellite
 Speed is less than that of polar orbiting satellite
 Scans a restricted (and fixed) area of the Earth’s surface only
 Applications: telecommunications generally, cable and satellite
TV, radio, digital information, etc.
 Satellite is in continuous contact with transmitting/receiving aerial
 Aerial can be in a fixed position

AQA A-level Physics (14 decks)

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