Properties of Waves and Sound

Barton Spring 2014 Honors Physics

Difference between wave motion and particle motion:

• Both carry energy• Particles move and carry energy

through a transfer of matter• A wave is a disturbance that

carries energy through matter or space

Mechanical waves: (like sound)

• Require a medium through which to travel–ie: water, air, ropes, spring–CANNOT travel in a vacuum

• Pulse – single wave

Longitudinal wave - vibrates parallel to direction of wave’s motion Sound waves

Mechanical waves:

• Transverse wave - vibrates perpendicular to direction of wave’s motion

http://nanobioart.com/members/ageorge/

Mechanical waves:• Surface waves – characteristics of both

transverse and longitudinal waves; particles move parallel and perpendicular to direction of wave motion

Equilibrium position (rest position)

Wave calculations:

dv

t

Tf

1

v f

Wave behavior:• Speed of wave depends only on the medium it

passes through (not amplitude or frequency)

• Incident wave – wave that strikes a boundary• Reflected wave – returning wave that has

bounced back from a boundary• faster wave speed slower wave speed --- reflected

wave is inverted• slower wave speed faster wave speed --- reflected

wave is not inverted• http://paws.kettering.edu/~drussell/Demos/reflect/reflect.html <---- demos of waves on rope

Wave behavior: • Principle of Superposition – displacement of a medium caused by 2 or more waves is the sum of the displacements caused by individual waves

• Interference – result of superposition of 2 or more waves

• http://paws.kettering.edu/~drussell/Demos/superposition/superposition.html <---superposition videoshttp://www.circleofoneness.org/ether.html

CONSTRUCTIVE

DESTRUCTIVE

Wave behavior:• Refraction – change in direction of waves at

the boundary between two different mediums, bending of the wave

http://www.crd.bc.ca/watersheds/protection/geology-processes/Waves.htm

Perceiving sound:• Pitch – depends on

frequency• Loudness – depends on

amplitude– Sound level – measuring

scale of amplitudes– Decibel (dB) – unit for

measurement of sound level

• Medium determines wave speed http://raider.mountunion.edu/~miskeljp/ds/schedule.htm0

Doppler effect:

• Doppler effect – frequency shift due to sound source movement– Closer/towards higher frequency– Further/away lower frequency

• Equation:• Song: http://imagine.gsfc.nasa.gov/YBA/M31-velocity/Doppler-shift-3.html

Think about it:If the source and observer are moving towards each other, the waves get bunched together and the frequency goes up.If the source and observer are moving further apart, the frequency will decrease as the waves get stretched apart.Keep this in mind as you apply the equation!