Waves and Sound

Wave

*vibration that travels thru a material and transmits energy* 

* *Created by a disturbance in the material/ medium* 

Transverse wave

particle motion is perpendicular to direction of wave motion

Longitudinal wave

particle motion is parallel to direction of wave motion

water wave

 a combo of longitudinal and transverse motion 

__*Wavelength*__ λ

Distance between any two successive points in phase

__*Amplitude*__ A

Max displacement of a particle from its rest position

__*Period*__ T

Time for 1 full vibration cycle 

* Time b/t oscillations in a wave
* Distance b/t 2 waves

Frequency

Inverse of period # of cycles/sec

* Hm oscillations/ waves we have per unit time

Phase

Refers to a particular point in the cycle of a wave

Calculating period & frequency: 

both are inversely proportional to each other

wavelength and frequency

when frequency is high, wave length short

* How does tension affect wave speed? 

* Speed of waves travelling in a string is controlled by tension 
* High tension = high speed 
* Low tension = low speed 

How does damping (aka frictional forces in a material) affect the amplitude of a pulse?

reduces it

How does damping in real materials affect the energy of a wave?

reduces it

What happens when wave reflects off of a loose and fixed end (bounce off): 

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* Loose: waves goe back and forth, Wave comes back not invertedly; comes back on same side
* Fixed: goes to one side and flips around the opposite way, reflect or flip 180 degrees, this is what should be drawn, Wave comes back invertedly

__*Interference/ overlapping waves:*__

* when 2/ more waves meet while travelling in the same medium

__*Net displacement (amplitude):*__

* sum of the amplitude of the waves 
* Constructive or destructive interference 
* Creates standing waves and beats

__*CONSTRUCTIVE INTERFERENCE*__

* Larger displacement (larger amplitude) 
* Crest overlaps crest 
* Trough overlaps trough 

* __*Resonance (Constructuve Interference)*__ 

* When an object vibrates at a particular f 
* Ex: strings, musical instruments 
* phenomemnen when an object is made to vibrate at its natural frew by a nearby obj vibrating at the same frequency 

This forced vibration is associated with high amplitudes of vibration die to tje extra energy, which may cause destruction of the object 
* Vibrations and sounds: 
* Vibration: mechanical motion oscillations point 
* Object suspended on a screen=

Vibrates at exact same frequeounce natural frequency; match the natural freq to cause it to vibrate = resonance 

Smae length = same natural frequency = resonance 

Red one matches same freq as black one causing it to vibrate 

Mini amphitheatres sound properties are used to amplify the sound

__*Sympathetic resonance:*__

* when one vibrating object induces a vibration in another object 
* Soldiers dont walk in formation across bridges 

__*DESTRUCTIVE INTERFERENCE*__

* Smaller displacement (smaller amplitude) 
* Crest overlaps trough 
* displacement/ amplitude is reduced 
* Crest cancels trough 

__*BEATS:*__

* Interference 
* Overlapping waves of different f (frequences) 
* Music: interference creates “beats”, changes in loudness and softness
* Red: wave 1 
* Blue: wave 2
* Green: Beat pattern
* Red and blue combine to form 
* High amplitude = LOUD 
* Low amplitude = *soft*

__*STANDING WAVES*__

Interference When 2 overlapping waves travelling in opposite direction have the same frequency

Standing waves are prod when equal wavelengths and In phase, constructuctive Out of phase (opposite, crest and trough), destructive Vibrating string gets reflected off fixed end, when this happens, depending on freq of vibration, faster vibration = more nodes, send wave, reflect it, complete destruction, (nodes) then constructive interference (anti nodes) Slowest frequency = first harmonic 2 antinodes = double freq 3 antinodes = tripled freq Nodes Spacing of nodes = equally spaced, in terms of wavelength it is ½ a wavelength 1 antinode = ½ a wavelength long Theyre oscillating back and forth

* have to have fixed point send same freq of wave, reflect off fixed/ free end, nodes (fixed; stand still), anti nodes (oscillate; back and forth)
* built up as waves move back and forth; waves that appear to not move but are an addition of the waves bouncing back and forth; adding and subtracting 
* Green wave seems stationery; but is actually moving; interference

nodes

points that have no displacement, 0 amplitude

* If two identical waves exist on the same string but traveling in opposite directions the result can be standing waves in which some points never have a deflection

antinode

large, moving displacements (maximum amplitudes)

* Some points oscillate between plus and minus the maximum amplitude

Standing waves provide _____ on musical instruments.

the notes, When a string is secured at both ends and plucked or hit the generated waves will travel along the string and be reflected and set up standing waves. 

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Echolocation

* sound waves reflecting off objects and when they come back, they can figure out what they are looking at 
* Waves hit other waves; overall either becomes larger/ smaller

__***Wave interactions:***__

 when wave interacts with object, or hits another wave

Wave interaction with wave:

* Constructive and destructive interference
* law of super position
* standing waves

interference

two waves interacting

__***Constructive interference:***__

when 2 waves come twd each other; results in 1 big wave

__***Destructive interference***__

* waves come from either side and cancel each other out; destroying the size of the wave

Wave interactions w/ object

* Reflection at fixed and free (loose) ends

reflection

*  happens; wave bounces back 

what type of wave is sound

longitudinal, pressure wave

what regions is sound made up of

high pressure: compressions

low pressure: rarefractions

what cannot sound travel in, but only light can travel in

empty space (vacuum)

frequency in sound:

pitch

intensity in sound:

loudness measured in decibels

what is sound intensity measured in

W/m^2

The human ear is incredibly versatile and can detect sound between

1 x 10^-12 W/m^2 up to 100 W/m^2

logarithm scale for intensity:

gives us the exponent to which the base must be raised to yield the given power., increases by a factor of 10, each dB step on decibel scale = increases by factor of 10

speed of sound in air depends on

temperature (and pressure)

echo

sound coming back, its timing determines how far the reflector is

in echo time, the sound has travelled

2x the distance

sound

longitudinal pressure wave caused by vibrations that needs a medium like air to travel in

mach 1

moving at speed of sound, wave fronts pile up forming a shockwave of high pressure

supersonic

travelling faster than mach 1 = bowwave formed

subsonic

traveling below, slower than, mach 1

doppler effect for a moving sound source

based on longer wl = lower f, shorter wl = higher f

what happens when wavefronts are pushed closer together as a car moves twaords you?

u hear a higher frequency

what happens when wavefronts are farther apart as the car moves away from you?

u hear a lower frequency sound