Physics Sg Lab Report

• Doppler effect: observer behind source hears lower pitch (longer wavelength)[pic 1]

                     observer in front of source hears higher pitch (shorter wavelength)

• sound waves are more commonly shifted than light waves
• p waves- fastest of 3 (longitudinal, pressure, can go through liquid)
• s waves- 1/2 as fast as ^ (transverse, secondary, can’t go through liquid)
• L waves- slowest of 3 (combo, L= s + p) its amplitude determines the Richter magnitude of an earthquake
• L = travel on surface // S and P travel on surface OR underground
• categorized in different ways:

1. how they travel

• matter or mechanical waves- must move through substances/ material (like earthquakes)
• energy or electromagnetic waves- can pass through a vacuum (light, heat)

1. how they’re generated

• longitudinal- parallel// matter waves// sound + shock waves// can propagate in solids, liquids, & gases
• transverse- perpendicular// energy waves// all forms of electromagnetic radiation (gamma, UV, when a crowd does the wave)// can propagate only in solids

• transmission medium- what wave passes through (earthquake=ground; music= air) determines speed of wave
• interference does not destroy the component waves. they mix, un-mix, and continue (ex. headlights)
• incident wave enters at the same angle that reflected wave bounces off
• high impedance = out of phase = most energy bounces back

Ch 14

• all sounds are caused by a vibration of some kind and speed of sound is generally greatest in solids

• sound waves in gases and liquids are primarily longitudinal
• sound waves in solids can have both transverse and longitudinal components bc intermolecular interaction in solids are much stronger// solids > liquids > gases in elasticity

• nodes- points of completely destructive interference
• antinodes- points of completely constructive interference
• standing waves- other waves transmit energy not matter// this doesn't transmit energy or momentum
• pure standing waves are formed by only 2 things: tuning fork and electronic keyboard// has a pattern
• noise is different from standing wave bc there is no pattern
• sympathetic vibration- an oscillation induced in an object by indirectly driving at its fundamental frequency
• conditions for resonance: the wavelength must have a whole number of wave segments fit on the string

• segments- the portion of the string between adjacent nodes

• when string is plucked in middle it vibrates at natural frequency (lowest freq that can sustain a standing wave)
• fundamental frequency = resonant = natural = 1st Harmonic// things can have more than 1 natural frequency
• amplitude = loudness// frequency = pitch/ note
• audible region = 20 - 20k Hz// there is a limit in the sound spectrum (one gigahertz)
• frequencies lower than 20 = infrasonic range (ie. nature, earthquakes)
• higher than 20k = ultrasonic// can travel for km in water so used in sonar// (ie. crystals, seafloor imaging)
• audibility threshold- quietest sound you can hear// pain threshold- loudest sound not producing pain
• intensity- the amount of energy entering an area in a certain amount of time
• intensity level- comparison of a sound’s loudness to a standard (that standard = audibility threshold)
• both the loudness AND duration of a sound affect hearing loss
• sonic boom- when something’ s traveling at speed of sound, a large # of waves overlap & produce many points of constructive interference which form a shock wave & when the shock wave passes over someone, the large concentration of energy produces a sonic boom// doesn't only occur when plane breaks sound barrier
• Mach- number greater than one indicates supersonic speed and less than one indicates subsonic. Number 2 indicates a speed twice the speed of sound