Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics Year 13 > Chapter 17 - Oscillations and SHM > Flashcards

Chapter 17 - Oscillations and SHM Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

define oscillatory motion

A

“oscillating motion occurs where an object starts in an equilibrium position and a force is applied, causing it to oscillate either side of its equilibrium position”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

explain the ‘phases’ of oscillatory motion

A
  • an object is displaced from its equilibrium position
  • it accelerates towards the equilibrium position and decelerates once it’s passed it
  • it reaches its maximum displacement the other side of the equilibrium position and the process repeats
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define displacement and amplitude, give their symbols and units

A

Displacement - x/m - Distance with respect to direction from its equilibrium position

Amplitude - A/m - Maximum displacement from equilibrium position

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

define period, frequency and phase difference, give symbols and units

A

Period - T/s - time taken to complete one full oscillation
Frequency - f/Hz - number of complete oscillations per unit time
Phase difference - Phi/ radians - the difference in phase of the cycles of the oscillations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

define angular frequency

A

“angular frequency describes the motion of an oscillating object through the rate of change of angle”

angular frequency = 2(pi)/period

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what are the equations for angular frequency

A

Omega = 2(pi)/t
Omega = 2(pi)f

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

give the equation for SHM and identify the main points

A

a = (-)(omega^2) x

where omega^2 is constant:
- acceleration is directly proportional to displacement
- it acts in the opposite direction (towards the equilibrium position)
- maximum acceleration occurs at maximum displacement (amplitude)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

give the three main features of SHM

A
  • an acceleration-displacement graph has a constant gradient pf Omega^2
  • frequency and period are constant
  • period of a pendulum in SHM is independent of amplitude
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe the practical used to determine the frequency and period of an object in SHM

A
  • set up a pendulum on a clamp stand or a spring with masses attached to a clamp
  • pick a point as a fiducial marker
  • set the pendulum swinging or spring oscillating and time n oscillations using the fiducial marker to help
  • divide the time by n to calculate the period of an oscillation
  • repeat for different amplitudes
  • calculate an average
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what shape are the graphs for SHM (displacement against time)

A
  • sinusoidal
  • if there are no energy losses Amplitude is constant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are the two possible shapes of a displacement-time graph for SHM

A
  • if starting from max displacement then cosine shape
  • if starting from equil position then sine shape
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

assuming we start from max displacement what is the shape of the velocity time graph for SHM

A
  • the derivative of cosine = -sine
  • so a -ve sine graph
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

assuming we start from max displacement, what is the shape of the acceleration time graph for SHM, what is important about this

A
  • the double derivative of Cosine = -cosine
  • so a is directly proportional to -x
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are the equations linking displacement and time for SHM

A

X = Acos(omega*t)
- if starting from max displacement
- if ans is -ve then it is on the other side of the equil position

X = Asin(omega*t)
- if from equil position
- assign one side +ve and one side -ve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is the equation for SHM linking velocity and displacement, amplitude and omega, what is the Vmax equation

A

V = +- omega Sqrt(A^2 - X^2)

Vmax = omegaA
- Because max velocity occurs at equil position (X=0)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

define damping

A

“an oscillation is damped when an external force that acts on the oscillator has the effect of reducing the amplitude of its oscillations”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are the key points about light damping, give an example

A

light damping:
- low energy losses
- period almost unchanged
- amplitude gradually decreases

e.g. air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what are the key points of heavy damping and give an example

A

heavy damping:
- higher energy losses
- period increases slightly
- amplitude decreases significantly

e.g. water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the key points of very heavy damping and give an example

A

Very heavy damping:
- no oscillatory motion
- slowly returns to equil position

e.g. syrup

20
Q

what generally happens to the kinetic energy of the oscillator in damping

A

KE —> other forms (usually heat)

21
Q

what do the graphs of the types of damping look like

A
  • light damping = sinusoidal but decreasing amplitude (exponentially)
  • heavy damping dips below the x axis comes slightly above then back to rest
  • very heavy damping looks like a -ve exponential
22
Q

what is a free oscillation

A

“a free oscillation is where a mechanical system is displaced from its equilibrium position and oscillates without external forces”

frequency = natural frequency

23
Q

what is a forced oscillation

A

” a forced oscillation is one in which a periodic driver force is applied to an oscillator”

freq = freq of driver

24
Q

what is resonance

A

“Resonance occurs where the driving frequency is equal to the natural frequency of the object, this causes amplitude to increase dramatically”
“Amplitude at this point is at a MAXIMUM”

25
Q

describe Barton’s pendulum experiment

A
  • a wire is fixed across two points
  • D is a heavier brass bob pendulum
  • there are a number of different lengths paper cone pendulums
  • D is set swinging, acting as a driving force
  • if a pendulum has the same length as D it will resonate and have a much greater amplitude than the other pendulums
26
Q

what can we say about the energy in a system of an object moving with SHM

A
  • total energy remains constant assuming no energy losses
27
Q

describe the energy transfers that occur in an oscillation of a pendulum

A
  • at the amplitude the object has no KE, only potential energy, in this case GPE
  • as the pendulum falls it loses GPE but gains KE
  • as it moves through the equilibrium position, it has maximum KE and no GPE
28
Q

what are the differences in the sources of potential energy between a pendulum and a mass-spring system

A

if the mass-spring system is vertically:
- potential energy is GPE and Elastic Potential

if the mass-spring system is horizontally
- potential energy is only Elastic Potential

29
Q

what does the graph of energy against displacement look like for an object in SHM

A
  • two parabolas
  • one -ve, one +ve
  • the +ve shaped parabola is Ep such that at max displacement, Ep is max
  • the -ve shaped parabola is KE such that at max displacement, KE = 0
  • total energy remains constant as a line running across the top
30
Q

explain a simple demonstration of energy transfer in SHM

A
  • spring and glider on an air track
  • compress spring
  • Elastic potential = 1/2 k X^2
  • this is transferred to the kinetic energy of the glider (1/2 mv^2)
31
Q

how can the air track demonstration explain the shape of the graph

A

at any point

KE = total energy - Ep
total energy = Ep max
Ep max = 1/2 k A^2

so
KE = 1/2 k A^2 - 1/2 k X^2
KE = 1/2 k (A^2-X^2)
so both KE and EP have parabola shapes

32
Q

what do the Ep and KE against time graphs look like against time for a pendulum

A

if pendulum starts from 0 displacement:
- Ep-time graph is like sin but only positive so Mod(sin)
- KE-time graph is like V^2 so cos^2, in other words a cos graph shifted up

33
Q

give some examples of where resonance is used

A
  • clocks use the resonance of a pendulum or quartz crystal to keep time
  • musical instruments have resonant casings and the air column inside instruments resonates
  • tuning circuits use resonance e.g. car radios
  • MRI scanners
34
Q

what does the graph of Amplitude of oscillation against driving frequency look like, give its key features

A
  • a number of lines which rise up to a peak then drop away but not a smooth parabola
  • the lines represent different amounts of damping
  • higher damping gives a lower line with a broader peak at a lower frequency
  • the peak of the highest line corresponds to F0, the natural frequency of the object
35
Q

describe the effect of damping on resonance

A

As the amount of damping increases:
- Amplitude of vibration at any frequency decreases
- frequency of Max amplitude is lower
- peak becomes flatter and broader

36
Q

describe how an MRI scanner works

A
  • surrounding the scanner there are superconducting electromagnets and coils to produce radio waves
  • These provide a very strong magnetic field
  • hydrogen nuclei behave like tiny magnets and precess (sort of spin thing)
  • when radio waves interact with them they resonate
  • once the nuclei stop resonating they release the energy as different wavelength radio wave photons that are detected
37
Q

Define SHM

A

an oscillatory motion where the acceleration of the oscillator is directly proportional to its displacement
and is directed towards a fixed / equilibrium point.

+ draw a graph

38
Q

what does the defining SHM graph look like

A

a graph of a = -w^2x
so effectively y = -x but with gradient -w^2

39
Q

what to remember to put when talking about the effect of amplitude changes on SHM

A

period is independent of amplitude

40
Q

in what direction does the resultant force act on an object in SHM and why

A

towards the equilibrium position:
reason one:
- there are two forces acting, tension and weight, these cancel to make the horizontal force
reason two:
- the only acceleration occurs towards the equilibrium position therefore that is the direction of the resultant force

41
Q

what can we derive from a v^2 against x^2 graph

A

v^2 = w^2A^2 - w^2x^2

so
y-int = (vmax)^2
grad = (angular frequency)^2

42
Q

what does a kinetic energy against time graph look like for SHM (if starting from max displacement)

A

like a sin^2(x) graph because if
v = -sin(x) then
Ek = f((-sin^2(x))
it looks like a cos graph shifted up

43
Q

what is the only thing that affects the period of a pendulum in SHM

A

the length of the pendulum

44
Q

is the net force acting on a mass in a mass-spring system ever equal to its weight

A

ONLY when it passes through the equil point

45
Q

what is the major difficulty in measuring angles of swing and period in an investigation and how can we solve it

A
  • the angle of swing decreases with time due to the damping effect of air resistance
  • to solve this you can measure a fraction of a swing (e.g. 1/4 of a swing) ACCURATELY using a DATA LOGGER and scale up to find period
46
Q

where can resonance be a nuisance

A
  • washing machines can have casings that resonate and cause loud vibrations
  • wind/walkers can cause bridges to resonate
47
Q

How to calculate the period of a simple pendulum when given length

A

T = 2(pi) sqrt(l/g)

Physics Year 13 (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions