Vibrations and Waves

Oar in Water Wings of a Bee Electrons in an Light Bulb Water Waves Sound Waves Light Waves “Wiggles in Time”“Wiggles in Space”

Vibrations and Waves Waves transmit energy and information. Sound and Light are both waves.

Simple Harmonic Motion... …is to-and-fro vibratory motion....results in sine curves. Examples: –metronome –mass on a spring –pendulum

Sine Curves Amplitude - distance from the baseline to the crest of a wave Wavelength - the distance from the top of one crest to the top of the next one

Wave Description Period - the time required for one vibration measured in seconds Frequency - number of vibrations per unit time measured in Hertz Bowling Ball Example

Wave Description Bowling Ball Example

Question: If you double the frequency of a vibrating object, what happens to the period? a) the period doubles b) the period stays the same c) the period is cut in half d) not enough information is given to answer this question.

What is the frequency in vibrations per second of a 60-Hz wave? What is its period?

What is the frequency in vibrations per second of a 60- Hz wave? Answer: 60 cycles per second What is its period? Answer: 1/60 second

Wave Motion medium - the stuff that carries the wave Waves Medium water waves water waves on a rope rope stadium waves people sound air light space (vacuum)

Wave Speed... the speed with which waves pass by a particular point e.g. the speed of a surfer It depends only on the type of medium. Wave Speed = Frequency  Wavelength

If a water wave oscillated up and down three times each second and the distance between wave crest is 2 m, what is its frequency? What is its period? What is its wavelength? What is its wave speed?

If a water wave oscillated up and down three times each second and the distance between wave crest is 2 m, what is its frequency? Answer: 3 Hz What is its period? Answer: 1/3 second What is its wavelength? Answer: 2 m What is its wave speed? Answer: 6 m/s

Transverse Waves side to side vibration in a direction perpendicular to the wave's motion Examples: –water waves –waves on a rope –string musical instruments

Longitudinal Waves back and forth vibration in a direction parallel to the wave's motion Examples: –slinky waves –sounds waves

INTERFERENCE Constructive or destructive interference results when waves add. Standing Waves - wave pattern produced from interfering waves –Examples Vibrating Strings Organ Pipe

Waves

Constructive Interference occurs when waves are in phase, that is when crests are superimposed and troughs are superimposed.

Destructive interference occurs when waves are out of phase, that is when crests are superimposed with troughs.

Standing Waves

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DOPPLER EFFECT the change in wavelength due to motion of the source "Wheeeeeeeeeeee…….Oooooooooooooo” Example: –moving cars and trains

DOPPLER EFFECT

BOW WAVES Waves in front of moving object pile up. The familiar bow wave generated by a speedboat knifing through the water is a non-periodic wave produced by the overlapping of many periodic circular waves. It has a constant shape.

SHOCK WAVES Just as circular waves move out from a swimming bug, spherical waves move out from a flying object. If the object flies faster than the waves, the result is a cone-shaped shock wave. There are two booms, one from the front of the flying object and one from the back.

SHOCK WAVES

Class Problem Dipping a finger in water faster and faster causes the wavelength of the spreading waves to a) increase b) decrease c) stay the same d) not enough information is given

Class Problem In the standing wave shown, what is its amplitude? What is its wavelength? How many nodes are there?

Class Problem In the standing wave shown, what is its amplitude? What is its wavelength? How many nodes are there? The amplitude of the wave is 10 centimeters; the wavelength is 1 meter; and there are 6 nodes.

What determines the speed of a wave? (a) the frequency (b) the wavelength (c) the amplitude (d) the period (e) the medium of transmission

A skipper on a boat notices wave crests passing his anchor chain every 5 seconds. If the wave crests are 15 m apart, what is the speed of the water waves in m/s? (a) 5 (b) 15 (c) 75 (d) 10 (e) 3

For a medium transmitting a longitudinal wave, the areas of the medium where the density of the medium is temporarily increased are called (a) rarefactions (b) compressions (c) density holes

Class Problem A train whistle at rest has a frequency of 3000 Hertz. If you are standing still and observe the frequency to be 3010 Hertz, then you can conclude that... a) the train is moving away from you. b) the train is moving toward you c) the sound from the whistle has echoed d) not enough information is given

What dictates the frequency of a sound wave? (a) wavelength (b) medium (c) source of the sound (d) speed (e) amplitude

When you move away from a fixed source of sound, the frequency of the sound you hear (a) is greater than what the source emits (b) is less than what the source emits (c) is the same as what the source emits

Sonic booms from a plane are produced (a) because the plane breaks through the sound barrier (b) when the plane reaches the speed of sound (c) by the plane traveling faster than the speed of sound (d) by the plane traveling slower than the speed of sound