introduction. how does sound move from one place to another? is there sound in outer space? if...
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Introduction
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How does sound move from one place to another?
Is there sound in outer space?If waves continuously crash on the beach, why doesn’t the ocean pile up on the coast?
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Waves we can see (Mechanical Waves)◦ Waves on water◦ Waves on a string◦ Waves in springs◦ Traffic◦ Others?
Waves we can’t see (Electromagnetic & other)◦ Radio waves, microwaves◦ X-rays◦ Sound waves◦ Earthquakes?◦ Light waves
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Energy causes something to vibrate Vibration is a repeating back and forth or up and down motion◦A vibration is a wiggle in time◦Think of a bell ringing
A wave is a wiggle that moves in space◦A wave moving across the ocean◦Sound coming from a bell
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Observe the mass bouncing on a spring◦ Describe as many things as you can about what
you see.
Click here to see animation
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Spring with a massPendulum at low swing angles
Bicycle pedal
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Mechanical waves require a medium (mass)◦Particles are in motion◦There is a restoring force◦Due to inertia, the mass passes through the resting point to the other side
◦Can be described with a sine wave
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Do the wave!
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http://www.walter-fendt.de/ph14e/stwaverefl.htm
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TOC
Transverse: Wave moves medium moves
Longitudinal Wave moves medium moves
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•The wave crests are moving through the water at 1 m/s•The wave crests are 1 meter apart
•The bird sees a wave crest A right now. How long before it sees:•Wave crest B?•Wave crest C?•Wave trough D?
ABC
D
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•The PERIOD (T) of the wave is the time between two points on the wave that repeat the pattern
•What is the period of this wave?•The FREQUENCY (f) of a wave is how often the wave repeats itself in one second
•What is the frequency of this wave?
•Relationship between frequency and period: f = 1/T
ABC
D
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The SPEED (v) of a wave is equal to wavelength x frequency
v = f
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Frequency: f = 1/T
Period: T = 1/f ) Velocity: v = f
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Speed v m/sWavelength metersPeriod T secondsFrequency f Cycles/sec (Hertz)
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The spring completes one cycle in 0.5 s.◦What is its period, T?◦What is its frequency, f?
T = 0.5 sf = 1/T = 1/0.5s = 2 Hertz (Hz)
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A surfer feels a wave every 10 s. If they are 50 m apart, how fast are the waves moving?
v = f , so we need to find fF = 1/T = 1/10sSo, v = 50m/10s = 5 m/s
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Waves transfer energy without transferring matter
Mechanical waves require a medium
A continuous wave is a regularly repeating sequence of wave pulses