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A level Physics > Unit 3.1 - Circular Motion > Flashcards

Unit 3.1 - Circular Motion Flashcards

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1
Q

Definition of period in waves

A

Time for one complete cycle

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2
Q

Definition of frequency in waves

A

The number of cycles per second

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3
Q

When referring to circular motion, what is the same as saying “one complete cycle” in waves?

A

1 full rotation

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4
Q

Unit for period of rotation

A

s

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5
Q

Period of rotation (s)

A

The time it takes an object to complete 1 full circle

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6
Q

Frequency unit

A

Hz or s-1

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7
Q

Frequency (in terms of circular motion)

A

The number of rotations the object undertakes per second

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8
Q

What are radians?

A

Units for an angle

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9
Q

Definition of a radian

A

The angle at the centre of a circle where the arc is equal to the radius of the circle

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10
Q

What is 1 radian equal to?

A

About 57.3 degrees

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11
Q

Radian unit

A

rad

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12
Q

Why do we use radians as opposed to degrees?

A

Easier maths

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13
Q

Radians in 1 full circle

A

2π rad

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14
Q

Circumference of a circle

A

2πr

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15
Q

Half a circle in radians

A

π rad

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16
Q

Quarter of a circle in radians

A

π
— rad
2

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17
Q

180 degrees in radians

A

π rad

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18
Q

Converting from radians to degrees

A

Just remember that π = 180 degrees, and input this into the equation

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19
Q

Degrees to radians equation

A

Angle in degrees
———————— x2π
360

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20
Q

What do we leave radian calculations in terms of?

A

π

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21
Q

What is angular velocity also known as?

A

Angular frequency

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22
Q

What does our measurement the radian helps measure?

A

Th angle subtended (drawn out) by an object moving in a circle

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23
Q

Angular velocity/frequency symbol

A

ω

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24
Q

ω

A

Angular velocity/frequency

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25
Q

Angular velocity

A

The rate of change of angle measured in radians per second

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26
Q

Angular velocity equation

A

ω = angle
———
t

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27
Q

How is the angular velocity equation altered for a full rotation of time period T?

A

ω= 2pi
——
T

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28
Q

Which radian measurement is used for a whole circle?

A

2 pi

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29
Q

Equation for relationship between period and frequency

A

T = 1/f

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30
Q

Angular velocity equation involving frequency

A

ω = 2pif

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31
Q

Explain in detail what centripetal force is

A

Newton’s first law states than an object stays still or keeps moving in the same direction with the same speed unless a force acts upon it
If an object is moving in a circle, its direction is changing (even if it’s moving at a constant speed)
Since the direction is changing, there must e a force acting on it
F = ma (Newton’s second law), therefore the object must be accelerating
The forces that are acting on the thing that’s moving are known as centripetal forces

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32
Q

When whirling a hammer in a circle, describe its velocity

A

Will have a velocity at a tangent to the circle

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33
Q

What happens to the velocity of a hammer if its whirled at a constant rate?

A

The magnitude of the velocity won’t change, but the direction is constantly changing

34
Q

How come a hammer being whirled around is accelerated due to the centripetal forces?

A

The direction of the velocity is constantly changing, so the velocity is changing, so the hammer is accelerating due to a force

35
Q

What is the force provided by in a hammer being swung around and what does this mean?

A

Provided by the chain
So, force acts in the same direction

36
Q

What is constant and what isn’t in centripetal acceleration (when spinning at a constant rate)?

A

Magnitude = constant
Path = not constant

37
Q

What is constant when something is spinning at a constant rate, even though the object is accelerating in a certain direction? Which direction is this?

A

Speed = constant
It accelerates towards the centre of the circle

38
Q

Centripetal force

A

Causes centripetal acceleration, which is always directed towards the centre of a circular path

39
Q

What does a centripetal force keep an object doing?

A

Moving in a circle

40
Q

What would happen to a spinning object once the centripetal force is gone?

A

It would accelerate in a straight line

41
Q

Is centripetal force a type of force?

A

No

42
Q

If centripetal force isn’t a type of force, what is it?

A

It’s the name given to a force that causes an object to move n a circle - the force is provided by a type of force

43
Q

Force that provides the centripetal force during the orbit of the earth around the sun

A

Gravitational

44
Q

Force that provides the centripetal force during a car cornering

A

Frictional

45
Q

Force that provides the centripetal force with a child on a swing

A

Tensional

46
Q

Force that provides the centripetal force with a child on a roundabout

A

Frictional

47
Q

Force that provides the centripetal force during an electron orbiting a nucleus

A

Electromagnetic

48
Q

Force that provides the centripetal force on a wind turbine

A

Tension

49
Q

Forces that provide the centripetal force during a car turning on a banked track

A

Component of normal reaction and friction (less friction than on a flat road due to the normal reaction force being there too)

50
Q

What is proof that force is directed towards the centre of a circle?

A

If we take the vectors of two velocities on a circle, their change in velocity is directed towards the centre of the circle

51
Q

Linear velocity on a circle equation to learn

A

v = 2pir/T

(2pir = circumference of a circle)
(T = time period for a full circle)

52
Q

What does a higher radius result in for an object with circular motion? Provided what?

A

A faster velocity
Provided that ω is constant

53
Q

Why does a higher radius result in a faster velocity for an object with circular motion?

A

More force is needed to keep it moving in a circle

54
Q

What happens to the acceleration of an object with circular motion when it has a higher radius and why?

A

Higher radius = faster velocity as more force is needed to keep it moving in a circle
Therefore, more acceleration is needed to keep it moving in a circle

55
Q

Equation relating angular and linear velocity

A

v = ωr

56
Q

Equation relating centripetal acceleration and angular velocity

A

a = ω^2r

57
Q

Centripetal acceleration

A

Acceleration needed to keep an object moving in a circle

58
Q

Acceleration needed to keep an object moving in a circle

A

Centripetal acceleration

59
Q

Derive a = v^2/r

A

Rearrange v = ωr to ω = v/r and place it into a = ω^2r

a = v^2/r

60
Q

Difference between v and ω

A

v = linear velocity

ω = angular velocity

61
Q

How do we derive the two equations for centripetal force?

A

Use the two expressions for acceleration in Newton’s second law equation (F = ma)

So, use a = ω^2r and a = v^2/r in F = ma to get

F = mω^2r
and
F = mv^2/r

62
Q

In which direction is the acceleration of circular motion?

A

Towards the centre of circular motion

63
Q

Discuss how their application of science enables cars to travel safely around curves

A

Appropriate surface
Appropriate tyre design for friction
Banking of road for contribution of normal contact force
Suspension set up

64
Q

What are the 2 equations for linear velocity to learn?

A

V = 2pir/T

And since f=1/T,

V = 2pirf

65
Q

Which forces make up the centripetal force in vertical circles?

A

Tension in the string
Weight of the object

66
Q

Equation for centripetal force at the top of a vertical circle

A

Centripetal force = weight + tension

67
Q

Equation for tension at the top of a vertical circle

A

Tension = centripetal force - weight

68
Q

What is constant on all points of a vertical circle and why?

A

Centripetal force
v is constant

69
Q

What needs to be higher at the bottom of a vertical circle and why?

A

Tension force in the string as weight acts in the opposite direction to centripetal force, and the centripetal force is constant

70
Q

Equation for centripetal force at the bottom of a vertical circle

A

Centripetal force = tension - weight

71
Q

Equation for tension at the bottom of a vertical circle

A

Tension = centripetal force + weight

72
Q

Where is there a higher tension on a vertical circle and why?

A

At the bottom
As tension needs to be higher to keep the centripetal force constant as weight now acts in the opposite direction

73
Q

Why does it feel like there’s more force at the bottom when spinning something around?

A

As there’s higher tension at the bottom

74
Q

What is revs.min-1?

A

A form of frequency

75
Q

What value do we use if something is “weightless” in a question?

A

a = 9.81ms-2

76
Q

What value do we use if something is at “minimum speed” in a question?

A

a = 9.81ms-2

77
Q

What value do we use if a question is asking for the “acceleration needed to just remain taut throughout the motion when rotating in a vertical circle”?

A

a = 9.81ms-2

78
Q

Degrees to radians

A

Degrees x 2pi/360

79
Q

Radians to degrees

A

Radians x 360/2pi

80
Q

Why is a car accelerating when moving in a circle?

A

Direction changing = velocity changing = accelerating

A level Physics (29 decks)

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