Sound Miscellaneous
Objectives
1. Explain how the speed of sound differs in solids and
gases
2. Describe forced vibration
3. Define resonance, Doppler Effect, bow wave, shock
wave, sonic boom and supersonic
4. Explain beats
5. Give examples of the Doppler Effect
Speed of Sound
• 340 m/s (760 mph)
• much slower than light
i.e. thunder and lightning
1. see lightning
2. count seconds until thunder
3. divide by 3
4. that is how far away the storm is from you (in km)
5. divide by 5 for miles
Speed of Sound
Speed of Sound and Different Media
• The more compact the medium - the faster sound travels
1. solids transmit sound fastest
2. gases transmit sound slowest
3. loud sounds do not travel faster than soft sounds
(amplitude does not affect speed)
4. high pitch sounds do not travel faster than low pitch sounds
(frequency does not affect speed)
• Sound travels faster in warm air
• even though cold air is more dense
• the molecules have more energy
• already moving quickly
Speed of Sound in Various
Media
Forced Vibration and Resonance
• Forced Vibration - when an object begins to vibrate
because of another vibrating object nearby
• All objects have a natural frequency
• Resonance - when an object is forced to
vibrate at its natural frequency
Forced Vibration
Beats
• result from overlapping of two
different frequencies of sound
• frequencies should be close
but not exact
• area of constructive
interference are loud
• area of destructive
interference are soft
Doppler Effect
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apparent change in the frequency of a wave
caused by motion of the source and/or the receiver
pitch gets higher as the sound approaches
pitch gets lower as the sound recedes
has nothing to do with loudness (amplitude)
used in radar and sonar
• speed of object determined as a function of the
change in frequency
Doppler Effect
Doppler Effect
Doppler Shifts
Bow Waves & Shock Waves
• Sometimes a source travels close to, at or faster than the speed
of the wave
• Bow Wave - when crests overlap in front of the source
• Shock Wave - when source moves faster than the wave
• Sonic Boom - shock wave caused by a supersonic object
• Supersonic - faster than the speed of sound
Bow Waves and Shock Waves