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LC Physics > centripetal force and gravity > Flashcards

centripetal force and gravity Flashcards

1
Q

abbreviations

A

in hback

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2
Q

centripetal force

A

a body is kept moving in a circle by a force called the centripetal force, acting towards the centre of the circle

F = mv²/r (incl notation)

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3
Q

the force required depends on:

A
  • the mass of the body
  • the speed of the body
  • inversely on the radius of the circle
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4
Q

uniform circular motion

A

if a body is in uniform circular motion, its velocity is constant in magnitude but not in direction, so it has acceleration

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5
Q

periodic time (T)

A

the time for one complete revolution

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6
Q

Radians

A

angles can also be measured in radians

If the circumference length is equal to the raidus, the angle is 1 radians

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7
Q

angle in radians formula

A

arc length / radius

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8
Q

radians and degrees

A

180° = π radians

= 3.14159 rad

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9
Q

equations

A

in hback

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10
Q

centripetal acceleration

A

if a body is moving in a circle the acceleration it has towards the centre of the circle is called the centripetal acceleration

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11
Q

gravity (Acceleration due to)

A
  • Ignoring air resistance, the acceleration due to gravity is the same for all bodies at the same place
  • A body falling freely experiences an acceleration g towards the centre of the earth
  • It is always downwards
  • 9.8 m/s⁻²
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12
Q

Kepler

A

in 1609 Kepler published his laws of planetary motion which discussed gravity. He published 3 laws

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13
Q

Kepler laws

A

1- The planets move in elliptical orbits round the sun as one focus

2- the line joining the sun and the planets sweeps out equal areas in equal time intervals

3- the square of the periodic time of a planet is proportional to the cube of its distance from the sun

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14
Q

Kepler’s Third Law

A

for the planets + the Moon, the square of the period of the orbit is directly proportional to the cue of the radius of the orbit

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15
Q

Kepler equations

A

hback

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16
Q

Derivations

A

hback

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17
Q

circular satellite orbits

A

hback

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18
Q

centripetal force

A

centripetal force = force of gravity

hback

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19
Q

period of an orbit

A

the time taken for a satellite to go once around the central body is called the periodic time or simply the period (T) of the orbit

20
Q

geostationary/parking orbit

A

a satellite that has the same period of orbit as the Earth and moves in the same direction is in a geostationary or parking orbit

21
Q

eg of geostationary orbits

A

communications satellites are geostatic to ensure uninterrupted TV signal

22
Q

Mandatory experiment

A
  • “g” by freefall method

- finding the period of a simple pendulum and hence finding a value for g

23
Q

circular satellite orbits eg

A

the Moon orbits the Earth and is its only natural satellite

24
Q

particle moving in a circle

A

tangential speed/linear speed

angular velocity

25
Q

tangential speed/linear soeed

A

v is called the tangential speed/linear speed of the object

v = velocity / ms⁻¹

26
Q

angular velocity

A

the rate of change of angle w/ respect to time

27
Q

angular velocity quantity, unit, symbol

A

scalar quantity

unit: rad s⁻¹ (rad per sec)
symbol: ω (greek letter omega)

28
Q

constant agnular velocity formula

A

angle traced out/time

29
Q

If an object is moving in a circular path of radius (r) with constant angular velocity (ω) and constant linear speed (v) then

A

v = rω

30
Q

proof of v = rω

A

in hback

31
Q

In what direction does centripetal force apply?

A

towards the centre

32
Q

Why GPS satellites are not classed as geostationary satellites

A
  • periodic time is not 24 hours

- not in the same place above the Earth

33
Q
  1. type of acceleration that the ISS experiences as it travels in a circular orbit around the earth
  2. what force provides this acceleration?
A
  1. Centripetal force

2. Gravitational force

34
Q

Force that makes us go down towards earth (what to label it as on questions)

A

weight

35
Q

Why do occupants of the ISS experience apparent weightlessness?

A

they are in freefall / ISS accelerating at same rate as occupants

36
Q

Period of a geostationary communications satellite

A

1 day / 24 hours

37
Q

forces on a ball on someones hand who’s spinning it in a circle

A
  • weight
  • normal
  • centripetal
38
Q

It is noted that the freq of the received radio signal changes as a satellite orbits Saturn. Why?

A

-Doppler effect due to relative motion between source of signal and detector

39
Q

type of force required to keep the ISS in orbit + direction of the force

A

centripetal force, towards centre of the orbit / towards the Earth

40
Q

An astronaut in the ISS appears weightless. Explain why

A

they re in a state of freefall, there is no contact force, only force acting is the force of gravity

41
Q

after an orbit, the ISS will be above a diff point on the Earth’s surface. Why?

A

ISS has a diff period to that of the earth’s rotation, not in geostationary orbit

42
Q

How many times does an astronaut on the ISS see the sun rise in a 24 hour period?

A

divide 24 hours by the ISS’s period (in hours)

43
Q

how a rotating object can be in equilibrium

A

constant angular velocity

44
Q

formula for v not in log table

A

V^2 = GM/R

45
Q

when doing centripetal calculations…

A

Use radians on calculator!!! The angle in the formulas are in terms of radians, not degree

Eg. angular velocity is rad/sec

LC Physics (25 decks)

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