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Physics Honors - Waves and Sound

Terms in this set (48)

simple harmonic motion
motion that repeats in a regular cycle when there is a restoring force that is proportional to the displacement (ex: springs and pendulums)
Hooke's Law
the more the spring is stretched or compressed, the greater the force

F = kx, where k is the spring constant
mg = kx
restorative force
the force caused by extending/contracting a spring
spring constant
a parameter that is a measure of a spring's resistance to being compressed or stretched
elastic potential energy
the energy of stretched or compressed objects
PE = 1/2kx^2
period
Amount of time it takes a wavelength to complete one oscillation or movement back and forth
T = 1/f
measured in seconds
period of a mass on a spring
T=2π √m/k
period of a pendulum
Tp=2π√L/g
frequency
the inverse of a period (oscillations per unit of time)
f = 1/T
measured in Hertz
Wave characteristics
frequency, amplitude, wavelength, crest, trough
oscillations
movement back and forth at a regular speed
transverse waves
the wave source vibration is perpendicular to the direction of the wave
longitudinal wave
the wave source vibration is in the same direction as the wave
wave speed
v = fλ
resonance frequencies
when an object is forced to resonate at it's natural frequency, the amplitude of the wave increases, sometimes to the point of destruction
wave pulse
a single bump or disturbance that travels through a medium
reflected pulses
when a wave pulse reaches a rigid boundary, the pulse will be reflected back

the amplitude will be inverted

the speed and wavelength of the reflected wave are the same as the original wave
wave interference
when the displacement of a medium by two or more waves is equal to the sun of the displacements, the waves combine to form a new wave, and the result of the sum of the two or more waves is interference
constructive interference
when the wave displacements are in the same direction and have a greater amplitude
destructive interference
occurs when the wave displacements are in the opposite direction, and the resulting wave has a smaller amplitude
standing wave
when a wave is timed just right, and the reflected wave interferes constructively with the incident wave
occur when there is resonance
node
A point on a standing wave that has no displacement from the rest position
antinode
A point of maximum amplitude on a standing wave
sound
a vibration that propagates as a wave through a medium
pitch
wave frequency (note)
loudness
wave amplitude
infrasonic
Sound waves with frequencies below 20 hertz
ultrasonic
Describes a sound of a frequency too high to be heard by the normal human ear---above 20,000 hertz
range of human hearing
20-20,000 Hz
sound waves are
longitudinal waves
sound wave travel at
340 m/s
sound travels at different speeds in different materials
fastest in air, specifically warm air
in water, sound waves travel
4x faster
in steel, sound waves travel
15x faster
why can't you hear someone in space?
no air
what travels faster, light or sound?
light, lightning
harmonics
- musical instruments use resonance to produce notes
- resonance varies to produce different notes (string length, pipe length, tension, etc.)
closed-pipe resonator
a resonating tube with one end closed to air
open-pipe resonator
a resonating tube with both ends open
beat frequency
The difference between the frequencies of the two combining sound waves that make a beat.
frequency of a string
f = nv/2L

n = # of harmonic
v = speed of wave on the string
L = length of string
f = frequency
frequency of an open pipe
fn=nv/2L

n = # of harmonic
v = speed of wave on the string
L = length of pipe
f = frequency
frequency of closed pipe
f = nv/4L

n = # of harmonic
v = speed of wave on the string
L = length of pipe
f = frequency
Doppler effect
An observed change in the frequency of a wave when the source or observer is moving
what happens to the pitch of a car when it drives away from you?
gets lower
what happens to the pitch of a car when it drives closer to you?
gets higher
what does it mean if a star has a red shift?
moving away
what does it mean if a star has a blue shift?
getting closer
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