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AQA A Level Physics > Simple Harmonic Motion (Need to add RP) > Flashcards

Simple Harmonic Motion (Need to add RP) Flashcards

1
Q

What is simple harmonic motion

A

A specific type of oscillation where there is repetitive movement back and forth through an equilibrium position.

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2
Q

What is the time period for each complete vibration in SHM

A

Time interval is the same

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3
Q

In which direction does the restoring force act

A

Always directed horizontally or vertically towards the equilibrium position

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4
Q

Relationship between distance from equilibrium and the restoring force

A

Directly proportional

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5
Q

Examples of SHM

A

Pendulum of a clock
Child on a swing
Mass on a string

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6
Q

Condition for SHM

A

The acceleration is proportional to the horizontal or vertical displacement
The acceleration is in the opposite direction to the displacement

a is directly proportional to -x

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7
Q

Acceleration of an object oscillating in SHM =

A

-(angular velocity^2 x displacement)

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8
Q

State the velocity, acceleration and force when the displacement = +max

A

Velocity = 0
Acceleration = -max
Force = -max

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9
Q

State the velocity, acceleration and force when the displacement = -max

A

Velocity = 0
Acceleration = +max
Force = +max

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10
Q

State the velocity, acceleration and force when the displacement = 0

A

Velocity = max
Acceleration = 0
Force = 0

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11
Q

What does the graph of acceleration against displacement look like

A

Straight line through the origin sloping downwards (like y = -x)

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12
Q

Velocity in terms of displacement

A

Rate of change of displacement

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13
Q

Acceleration in terms of velocity

A

Rate of change of velocity

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14
Q

What does a displacement-time graph look like, when oscillation start from equilibrium

A

Sine curve

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15
Q

What does velocity-time graph look like, when oscillation start from equilibrium

A

Cosine curve

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16
Q

What does acceleration-time graph look like, when oscillation start from equilibrium

A

negative sine curve

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17
Q

How are all the graphs derived

A

v-t graph derived from gradient of x-t graph
a-t graph derived from gradient of v-t graph

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18
Q

Equation for restoring force

A

Force = -kx
Where k is a constant.

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19
Q

What happens to the time period of the oscillation as spring constant increases

A

The spring will be stiffer so exerts a larger restoring force and the time period of the oscillation will be shorter

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20
Q

What does the time period of a pendulum depend on

A

Gravitational field strength, therefore would be different on different planets

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21
Q

sin theta in a pendulum =

A

approximately theta as the formula is limited to small angles (smaller than 10 degrees)

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22
Q

What is the restoring force of the pendulum

A

The weight component acting along the arc of the circle towards the equilibrium position and is resolved to act act at and angle theta to the horizontal x.

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23
Q

Why is it assumed the restoring force in SHM in a pendulum acts along the horizontal

A

Because of small angle approximation

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24
Q

Which equation do you use for situations such as liquid in a U-tube

A

The same as the equation for a simple pendulum as it can be modelled in the same way

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25
What energies are involved in the swinging of a pnedulum
GPE and KE
26
What energies are involved in the horizontal oscillation of a mass on a spring
Elastic potential and Kinetic energy
27
In a mass-spring system where is the max elastic potential energy
When the spring is stretched beyond its equilibrium position
28
What happens to KE when the mass in a mass-spring system is released
Mass moves back towards equilibrium position and it accelerates and causes KE to increase
29
When is KE at its max in a mass-spring system
At equilbrium position
30
When is EPE at its minimum in a spring system
At equilibrium position
31
What happens to KE and EPE once past the equilibrium position in a mass spring-system
KE decreases and EPE increases
32
When is the GPE max in a simple pendulum
At the amplitude top of the swing
33
What happens to KE when the pendulum is released
Pendulum moves back towards the equilibrium position and accelerates so the KE increases
34
What happens to the GPE as the height of the pendulum decreases
GPE decreases
35
What happens to both GPE and KE once the mass has passed the equilibrium position
KE decreases and GPE increases
36
What happens to the total energy of a simple harmonic system
It always remains constant and is equal to the sum of KE and GPE/EPE
37
Key features of an energy-displacement graph
Potential energy is at max at the amplitude and 0 at the equilibrium and is represented by U shape KE is 0 at amplitude and max at the equilibrium position and is represented by an n shape Total energy is represented by a horizontal straight line
38
Key features of an energy-time graph
KE and potential energy are always in complete opposite positions. e.g. max KE = min PE
39
What is damping (simple)
A resistive force that causes an oscillating object to stop oscillating such as friction and air resistance
40
What are the 3 types of damping
Light damping Heavy damping Critical damping
41
What direction does damping force act in
Opposite to velocity It is proportional to negative velocity
42
Damping (definition)
The reduction in energy and amplitude of oscillations due to resistive forces on the oscillating system
43
How long does a damping force last
Until the oscillator comes to rest at the equilibrium position
44
What happens to the frequency of damped oscillations as the amplitude decreases
The frequency DOES NOT CHANGE as the amplitude decreases
45
Light damping characteristics
The amplitude does not decrease linearly, but exponentially with time Lightly damped oscillating will oscillate with gradually decreasing amplitude Time period is the same
46
Features of a displacement-time graph for a lightly damped system
Many oscillations represented by a sine or cosine curve with gradually decreasing amplitude over time Height of curve decreasing in both positive and negative displacement values Amplitude decreases exponentially Time period is the same and peaks and troughs are equally apart
47
Critical damping characteristics
A critically damped oscillator returns to rest at its equilibrium position in shortest time possible without oscillating
48
Features of a displacement-time graph for a critically damped system
System does not oscillate so displacement falls to 0 straight away Fast decreasing gradient until it reaches the x axis When oscillator reach equilibrium, the graph is a horizontal line at x=0 for remaining time
49
Heavy damping characteristics
Takes a long time to return to equilibrium position without oscillating System returns to equilibrium more slowly than critical damping
50
Key features of a displacement-time graph for heavily damped system
No oscillations so displacement does not pass zero Slow decreasing gradient until it reaches x axis Once oscillator reaches equilibrium position, the graph remains a horizontal line
51
Difference between resistive force and restoring force
Resistive force opposes the motion/velocity of the oscillator and causes damping Restoring force is what brings the oscillator back to equilibrium position
52
When do free oscillations occur
When there is no transfer of energy to or from the surroundings. This happens when an oscillating system is displaced and left to oscillate
53
Free oscillation
An oscillation when there are only internal forces and no external forces acting and there is no energy input
54
Forced oscillations
Oscillations acted on by a periodic external force where energy is given in order to sustain oscillations
55
Why must a periodic force be needed to sustain oscillations in a SHS
To replace the energy lost in damping. The periodic force does work on the resistive force decreasing the oscillations.
56
What frequency does a free vibration oscillate at
Its resonant/natural frequency
57
What frequency do forced oscillations vibrate at
The same frequency as the oscillator creating the external, periodic driving force
58
Natural frequency (f0)
The frequency of an oscillation when the oscillating system is allowed to oscillate freely
59
Resonance
When the frequency of the applied force to an oscillating system is equal to its natural frequency, the amplitude of the resulting oscillations increases significantly
60
Why is amplitude greatest at resonance
Energy is transferred from the drive to the oscillating system most efficiently therefore the system transfers the max KE possible
61
Features of a driving frequency against amplitude graph / resonance curve
When f < f0 , the amplitude increases (f is the driving frequency, f0 is natural frequency) At the peak where f = f0 , the amplitude is at its max - resonance when f > f0, the amplitude starts to decreases
62
Effect of damping on resonance
Damping reduces the amplitude of resonance vibrations Height and shape of curve changes on the degree of damping
63
Effect of damping on the natural frequency
It remains the same
64
What happens to resonance graph as the degree of damping increases
Amplitude of resonance vibrations decrease - peak is lower Resonance peak broadens Resonance peak moves slightly to the left of the natural frequency when heavily damped
65
Overall effect of damping on the resonance and amplitude
Reduces sharpness of resonance and reduces amplitude at resonant frequency
66
What happens to resonant frequency at heavier damping
Resonant frequency becomes slightly less than f0
67
Examples of where resonance occurs
An organ pipe Glass smashing from a high pitched sound

AQA A Level Physics (23 decks)

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