Flashcards in Physics Unit 4: Waves Deck (15):

1

## Types of Mechanical Waves

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Mechanical Wave: the TRANSFER of ENERGY through a material due to vibration

1) Transverse Waves: a wave in which particles in the medium oscillate perpendicular to the direction of the flow of energy (aka energy propagation)

ex: particle is oscillating up and down while the wave motion is moving horizontally

- Do not occur in liquids of gases (light waves are an exception)

2) Longitudinal wave: a wave in which particles oscillate in the same direction as the flow of energy/energy propagation

ex: slinky, sound

-compression, rarefaction

^refer to the local pressure differences as the wave’s energy passes through the medium

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## Compression

### Compression: the region in a longitudinal wave in which the medium’s particles are CLOSE together →maximum density/high pressure

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## Rarefaction

### Rarefaction: the region in a longitudinal wave in which the medium’s particles are farther apart →minimum density/low pressure

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## Transverse Wave characteristics

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• Amplitude: the maximum displacement of a wave/vibrating particle from its equilibrium point (halfway between the max and the min) →metres (transverse wave)

• Crest: Maximum point of a transverse wave

• Trough: Minimum point of a transverse wave

Wavelength: the distance BETWEEN two similar points in successive identical cycles in a wave, such as from a crest to crest or trough to trough (similar to period but in meters) →lambda

-distance of one complete cycle

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## Phase

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Phase: in a continuous transverse or longitudinal wave, the x-coordinate of a unique point of the wave (same units as the wavelength→m)

Phase shift: a shift of an entire wave along the x-axis with respect to an otherwise identical wave (m)

- the amount that one waveform is displaced along the axis from an otherwise identical waveform -->transformations

-determine how much the wave has transformed (using wavelength)

ex: left a quarter of a wavelength = - lambda/4

Left = -

Right = +

In phase: the state of two identical waves that have the same phase shift (shown as one)

Out of phase: the state of two identical waves that have different phase shifts (the amount they are out of phase is equal to the phase shift)

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## Wave speed

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Wave speed (v): the rate at which a wave/energy is travelling through a medium; also a measure of how fast the energy in the wave is moving →m/s

v = Wavelength/period = length of one cycle/time for one cycle

v = f*wavelength (in m/s)

Speed of a wave along a string:

v = Square root (Force of tension/linear density)

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## Frequency

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Frequency (f): the number of complete cycles/waves that pass a point per unit time OR number of oscillations (up/down) per second, usually 1 s; measured in hertz (Hz)

Frequency = cycles/unit of time → f = 1/T

*short wavelength, high frequency

*long wavelength, low frequency

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## Period

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Period (T): the time for a vibrating particle to complete one cycle (time for one oscillation)

Period = time/unit cycle → T = 1/f

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## Longitudinal wave characteristics*

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• Amplitude: the maximum pressure it creates compared to the pressure of the non-disturbed medium

-->how far the slinky moves from its equilibrium point

Displacement-position graph: comparing the position to its equilibrium position

-if move to the left = going down/-

-if move to the right = going up/+

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## Factors affecting wave speed

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Efficient transfer = faster wave

• Rigid medium

• Tighter medium (string)

• Lighter medium (the linear density (mu) in a string (mass))

• High temperature

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## Linear Density (mu)

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• Linear density (mu): the mass per unit distance of a string; units are kilograms per meter (kg/m)

o Mu = m/L

(L is the length in meters)

(m = mass in kg)

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## Waveform

### • Waveform: the shape of a wave when graphed

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## Displacement-time

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Shows the displacement of a point as a function of time (point moves up then back down)

-can use displacement position graph and make displacement time graph by looking at what is happening next on the RIGHT

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## Displacement-position

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Snapshot of the wave at a particular point in time

-predicting what is going to happen next by looking behind the y axis/LEFT (moving down or up)

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