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Jen's B-Block > Circular Motion and SHM > Flashcards

Circular Motion and SHM Flashcards

1
Q

What is the term given to an object rotating at a steady rate?

A

Uniform circular motion

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2
Q

If an ball on a string is travelling in a circle in the vertical plane, where are the points of minimum and maximum tension?

A

Minimum tension at the top
Maximum tension at the bottom

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3
Q

Define centripetal force

A

The resultant force that makes the object move in a circle

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4
Q

Why do planes turn when at an angle?

A

The lift force is comprised of a horizontal and vertical component.
The horizontal component provides the centripetal force causing it to turn.

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5
Q

What kind of motion will a pendulum perform?

A

Simple harmonic motion

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6
Q

What is the period of oscillation?

A

The time for one complete cycle of oscillation.

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7
Q

If the graph of displacement is sin(x), what will the respective graphs of velocity and acceleration look like?

A

Velocity as cos(x)
Acceleration as -sin(x)

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8
Q

Describe a freely oscillating object

A

It oscillates with a constant amplitude because there is no friction acting on it.

(Its energy is constant)

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9
Q

What is natural frequency?

A

The frequency of free oscillations of an oscillating system.

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10
Q

What are forced vibrations?

A

Making an object oscillate at a frequency that is not it’s natural frequency

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11
Q

When does resonance occur?

A

When the frequency of driving force or oscillation matches the natural frequency of the system.

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12
Q

What is the outcome of resonance?

A

An increase in amplitude of the system’s oscillation.

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13
Q

What is damping?

A

The term used to describe the removal of energy from an oscillating system.

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14
Q

What are the three levels of damping?

A

Light
Heavy
Critical

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15
Q

Describe light damping of a system

A

The system oscillates over a long time frame before coming to rest.
The amplitude of the oscillations exponentially decay.

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16
Q

Describe heavy damping (over damping)

A

System not allowed to oscillate.

Slowly returns to equilibrium.

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17
Q

Describe critical damping

A

The oscillating system returns to the zero position of the oscillation after one quarter of a time period.

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18
Q

How do you convert degrees -> radians

A
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19
Q

How do you convert radians -> degrees

A
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20
Q

Define angular displacement

A

The angle through which an object in circular motion travels in a given time

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21
Q

How do you deal with rpm? (revolutions per minute)

A

÷60 to convert to rps (revolutions per second)

Then set rps = frequency

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22
Q

Define frequency

A

The number of complete oscillations per second

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23
Q

What is the equation for linear velocity?

A
24
Q

Why is an object in circular motion accelerating?

A

Its linear velocity does not change in magnitude

But is constantly changing in direction

25
Q

In circular motion which direction do the acceleration and centripetal force vectors act?

A

Always towards the centre

26
Q

What is the condition for circular motion to happen?

A

A velocity needs to be acting perpendicular to a resultant force

27
Q

What happens if…

Fcentri > Fmax

A

Circular motion does not happen

(Eg car skids off the road or moves to a higher radius)

28
Q

What happens if…

Fcentri max

A

Circular motion happens

(eg friction is large enough to keep car on track)

29
Q

What is Fcentri for an object at the top of the vertical circle?

A
30
Q

What is Fcentri for an object on top of a vertical circle?

A
31
Q

What is Fcentri for an object at the bottom of a vertical circle?

A
32
Q

How do you find out the minimum velocity for an object travelling in a vertical circle?

A

Set R=0 (or tension if ball on string)

And rearrange for v

33
Q

How do you find out the maximum velocity for an object travelling over a vertical circle? (eg car over a hill)

A

Set reaction R=0

Then rearrange for v

34
Q

When solving angled circular motion problems what are the 3 usual steps?

A
  1. Set vertical component of force = weight
  2. Work out horizontal component using trig
  3. Fcentri = horizontal component
35
Q

Why can’t a ball be swung around in a circle with the string horizontal?

A

There must be a vertical component of the tension to match the weight

Otherwise ball is not in vertical equilibrium

36
Q

What are the two conditions for SHM?

A
  1. Acceleration must be proportional to displacement
  2. Acceleration must be opposite to displacement
37
Q

How does the time period differ for the two pendulums?

A

Time period is independent of amplitude

38
Q

Define amplitude.

A

The maximum displacement of an obejct/particle/point from equilibrium position

39
Q

Label up the maximum and minimum velocities and accelerations on the simple pendulum…

A
40
Q

Label up the maximum and minimum velocities and accelerations on the mass spring system…

A
41
Q

Label up the maximum and minimum potential and kinetic energies on the simple pendulum…

A
42
Q

What are the kinetic energy, potential energy and total energy lines for one cycle of SHM?

A
43
Q

When do you use?

x=Acos(wt)

When do you use?

x=Asin(wt)

A

x=Acos(wt) -> displacement in SHM when x=A when t=0

x=Asin(wt) -> displacement in SHM when x=0 when t=0

44
Q

How do you calculate KEmax or PEmax or ET in SHM?

A
45
Q

What two factors affect the time period of a mass spring system in SHM?

A
  1. Mass on the end of the spring
  2. Spring constant (stiffness) of spring
46
Q

What two factors affect the time period of a mass spring system in SHM?

A
  1. Length between top of string and centre of bob
  2. Gravitational field strength
47
Q

What does the graph of energy against displacement look like in SHM?

A
48
Q

Does circular motion count as SHM?

A

When projected onto a flat surface, yes it does

49
Q

When an SHM system is lightly damped what happens to its amplitude and time period?

A

Amplitude decreases (as it loses energy)

But time period remains constant

50
Q

How is natural frequency determined for a mass spring system?

A
51
Q

How is natural frequency determined for a simple pendulum?

A
52
Q

What happens if the frequency of driving force is less than the natural frequency of a system?

f0

A

Low amplitude oscillations

With 0 phase difference.

53
Q

What happens if the frequency of driving force matches the natural frequency of a system?

f=f0

A

Resonance occurs

Large amplitude oscillations

π/2 radians out of phase

54
Q

What happens if the frequency of driving force is more than the natural frequency of a system?

f>f0

A

Low amplitude oscillations

With phase difference of π

55
Q

The graph below shows driven oscillations with varying frequencies.

Add two lines if the system is:

  1. Undamped (free oscillations)
  2. Over damped
A
56
Q

For Barton’s pendulum which two balls oscillate?

A

P and Y because they have the same length

So natural frequency of y matches frequency of driving force from P

Jen's B-Block (4 decks)

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