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Vibrations and Waves. the basis of sound and light. Pendulum. Back and forth motion of pendulum called simple harmonic motion (SHM) Period is time it takes to swing back and forth. Displacement is how far the pendulum moves from the centerline Period is dependent on string length
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Vibrations and Waves the basis of sound and light
Pendulum • Back and forth motion of pendulum called simple harmonic motion (SHM) • Period is time it takes to swing back and forth. • Displacement is how far the pendulum moves from the centerline • Period is dependent on string length • Period is independent of weight • Period is independent of displacement
Wave motion • Pendulum demonstrates the back and forth repetitive motion of a wave. • There are water waves, light waves, sound waves, and many more types of waves. • Waves move energy without a net movement of matter.
Source of Energy for Waves • Waves get their energy from vibration. • The back and forth motion of vibration causes the particles in the medium (water for an ocean) to move also resulting in wave motion.
Amplitude • Measure of strength of wave • distance from midpoint to crest or trough
Wavelength • distance between one crest and the next • is the symbol for wavelength
Frequency • describes movement of wave • number of vibrations per second • measured in hertz • period is time to make one complete cycle • frequency = 1 / period • period = 1 / frequency
Wave Speed • Distance between crests • Divided by the time between the crests • wave speed = frequency x wavelength • v = f
Relationship between frequency and wavelength for sound in air
Transverse Waves • Sine wave • motion of wave at right angles to movement of wave http://www.control.co.kr/java1/wave%20Trans/WaveTrans.html
Longitudinal Wave • particles move back and forth in direction of the movement of the wave
Superposition • When two waves occupy the same space, their amplitudes add together • The waves pass through each other • After their combination, they continue along their original path as if they had not combined for the moment. http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave2.html
Destructive Interference http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave3.html
Standing Waves • Reflection combines with incoming wave to produce portions of the wave that appear to be stationary • nodes are stationary • antinodes move the most http://www.physicsclassroom.com/mmedia/waves/swf.html
Doppler effect • if the wave generator is moving, the apparent frequency of the wave changes to a stationary observer • higher frequency as the center of the wave comes to you • lower frequency as the center of the wave moves away
Doppler effect • car horn • sirens • radar gun • light • increase frequency – blue shift • decrease frequency – red shift http://www.shep.net/physics/
Bow Waves • waves travel in all directions from the source of the wave (sound) • if the source of the sound is moving slower than the wave, the Doppler effect is created • higher frequency as sound approaches • lower frequency as sound moves away http://www.astro.ubc.ca/~scharein/a311/Sim/doppler/Doppler.html
Sonic Boom • Hear the movement of air not the sound from the object • Sonic boom formed all the time the object moves faster than the speed of the wave not just as it reaches the speed of the wave • Object does not have to make a sound to form a sonic boom • snapping towel