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Waves & Sound

Overview of Chapter 25 & 26

Emily Schreiner

on 4 February 2013

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Transcript of Waves & Sound

Waves And Sound Conceptual Physics What is a wave? Period: the time of one back and forth cycle; measured in seconds
Period = 1 / frequency

Frequency: how frequently vibration occurs; measured in hertz
Frequency = 1 / period Transverse wave: particles move in right angles to the wave
Wavelength: the distance from the top of one crest to the top of the next one
Amplitude: distance from the Equilibrium Line to the Crest/Trough
Crest: the high points of a wave
Troughs: the low points of a wave Wavelength = Wave Speed / Frequency Standing waves: nodes remain stationary

Node is a point along a standing wave where the wave has the least amplitude

Antinode: occur halfway between nodes, positions on a standing wave with the largest amplitudes Doppler effect: change in frequency due to the motion of the source (ex. an ambulance)
Blue shift: an increase in frequency
Red shift: a decrease in frequency Forced Vibration: the vibration of an oject that is made to vibrate by another vibrating object that is nearby. The sound board in a musical instrument amplifies sound through forced vibrations

Natural frequency: an objects own special set of frequencies, depends of elasticity and the shape of an object Resonance: occurs when the frequency of forced vibrations in an object matches the objects natural frequency, amplitude dramatically increases

Beats: A Periodic variation in the loudness of sound Longitudinal waves: particles move along the direction of the wave
Compression: a pulse of compressed air
Rarefaction: disturbance in air when pressure is lowered
Wavelength: distance between adjacent compressions and rarefactions What is a vibration? A vibration is a wiggle in time A wave is a wiggle in time AND space Example: A pendulum Example: A slinky Practice! 1. A butterfly beats its wings 12 times in 3 seconds. Find the frequency and the period. 2. Laura can fly 50 times around the world in 5 minutes. Find the frequency and the period. Answers! 1. Frequency: 4 Hz
Period: 1/4 seconds 2. Frequency: 1/6 Hz Period: 6 seconds Transverse Wave Wave Interference Constructive Destructive (cancellation) (reinforcement) Amplitudes are added... -when crests overlap crests
-when troughs overlap troughs Waves are "in phase" Amplitudes are subtracted... -when crests and troughs overlap Waves are "out of phase" Longitudinal Waves Simple Harmonic Motion: A back-and-forth repetitive motion Pitch: frequency of the sound
Infrasonic: sound waves with frequencies below 20 hertz
Ultrasonic: sound waves with frequencies above 20,000 hertz Properties of Sound Practice! 1. A wave is traveling at 10 m/s with a frequency of 5 Hz. What is the wavelength?

2. A slinky has a wavelength of 3 meters and a frequency of 12 Hz. What is the wave speed?

3. A pendulum is swinging 500 m/s! The pendulum completes 10 cycles in 50 seconds. Find the wavelength. Answers! 1. 2 meters
2. 36 m/s
3. 2500 meters LOUDNESS corresponds to the amplitude of a wave
In a longitudinal wave, amplitude can be thought of as the pressure of density of a compression. What the heck is it? A continuous phenomena. It happens when an object is traveling at the speed of sound; waves are compressed into a single shock wave! An example is the cracking noise from a bullet being shot. Quality of Sound Timbre: the make-up of how much of each harmonic or overtone is played in each note. It's what makes instruments sound different from one another. = M/S ________________ Hertz These should look familiar... SONIC BOOOOOOOOM! A larger example... wavelength For Closed Captioning: www.youtube.com/watch?v=Kg9F5pN5tlI Audiogram ...what do you know about it? For closed captioning:
www.youtube.com/watch?v=-d9A2oq1N38 What do you know about pendulum and slinkies? Write everything that you know about them AND be as scientific as possible.
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