unit 9, waves and sound - physics 11

waves and sound

vibration

a cyclical (or repeated) motion back and forth or around an equilibrium (or rest) position

wave

the transfer of energy in the form of vibrations from one location to another

transverse wave

a wave in which the energy of the vibrations is transferred in a direction that is perpendicular to the direction in which each molecule vibrates

compressions 

areas of high pressure in a longitudinal wave

rarefactions

areas of low pressure in a longitudinal wave

longitudinal wave

a wave in which the energy of the vibrations is transferred in a direction that is parallel to the direction in which each molecule vibrates

amplitude

max displacement from equilibrium

frequency

reciprocal of period

number of cycles completed each second

period

time required for each vibration to complete one full cycle

wavelength

distance between corresponding points on successive cycles of a wave

crest

max point of transverse wave

trough

min point of transverse wave

echolocation

the ability to determine the distance to an object by producing a sound and detecting the time required to hear its echo - can only be used to locate objects as long as, or longer than, wavelength of sound

interference

the process of generating a new wave when two or more waves meet

principle of superposition

at any point the amplitude of two interfering waves is the sum of the amplitudes of the individual waves

constructive interference

the process of forming a wave with a larger amplitude when two or more waves combine

standing wave (stationary wave)

interference pattern produced when incoming and reflected waves interfere with eachother

wave speed of a standing wave

0 because it is the difference between incoming and reflected waves

node

in a standing wave, the location where the particles of the medium are at rest

antinode

in a standing wave, the location where the particles of the medium are moving with the greatest speed

amplitude of antinode

twice the amplitude of original wave

mechanical wave

a wave that travels through a medium

sound waves

mechanical waves with frequencies that make them detectable through the ear

fundamental frequency (first harmonic)

the lowest frequency that can produce a standing wave in a given medium

when a source is moving away, observer at rest in a medium will detect

a lower frequency (+)

damping

a reduction in the amplitude of a wave as the result of energy absorption or destructive interference

resonance 

the increase in amplitude when the original waves and reflected waves are in phase causing a buildup of energy in the medium

interference does not affect…

wave direction and amplitude

in order to form a standing wave pattern in a medium that is open at one end and closed at one end…

the length of the medium must be an odd multiple of a quarter wavelength

in order to form a standing wave patten in a medium that is fixed at both ends (or free at both ends)…

the length of the medium must be a multiple of a half wavelength

beats

fluctuations in the sound amplitude (ie superposition) when two sound waves are heard together. The interference alternates between constructive (loud) and destructive (quiet). This occurs when there is a small difference between the frequencies of the two sounds.

when a source is approaching, observer at rest in a medium will detect…

a higher frequency (-)