Sound

Sound Waves  Longitudinal Waves (disturbance) that travel through a medium  Begins with a vibration  Carries ENERGY (like all waves)  Can travel through solids, liquids, & gases What wave causes Sound?

Sound Waves  Sound CANNOT travel in space  Sound waves are formed by the vibration of particles of matter  Since there is little or no matter in space, there are no particles to vibrate Why is there no sound in space?

Sound Waves  Temperature *C (celsius)  Nature or Type of the Medium (solid, liquid gas) What Determines the Speed of Sound?

Sound Waves  As the temperature of a medium increases, the speed of sound increases  The higher the temperature, the faster the particles of a medium vibrate  Speed of sound in air is 340 m/s at 15°C What happens to sound with different temperatures?

Nature of the Medium The more elastic the material, the faster sound travels Solids are more elastic than liquids Liquids are more elastic than gases –Speed of sound in water  1500m/s –Speed of sound in steel  5200 m/s The greater the density of a medium, the slower the sound

Sound Proper ties Intensity Pitch Timbre What are the Prope rties of Soun d?

Intensity (Loudness) The amount of energy in a wave Intensity/Loudness determines the amplitude of a wave The greater the intensity, the louder the sound Decibels – units used to measure the intensity of sound –Sounds over 120 decibels cause ear pain –Ear damage starts with as low as 85 decibels What is Intensity or loudness? What does intensity do? What is a decibel?

Pitch How high or low a sound is Frequency of a wave determines pitch - Higher the frequency, the higher the pitch Low pitch travel faster than high pitch Humans can hear sounds from 20 to 20,000 Hz Sounds over 20,000 Hz are ultrasonic Sounds under 20 Hz are infrasonic Thunder  less than 50Hz (Low Pitch) Whistle  close to 1000 Hz (higher pitch) What is pitch? What does frequency do to pitch? What does pitch do to wave speed? What frequency do human hear? What is ultrasonic and infrasonic? Examples of pitch:

Interactions Between Sound Waves Resonance Reverberation Music Noise Acoustics – the science of sound

Resonanc e All objects vibrate naturally at their own frequency Resonance occurs when the frequency of an object equals the frequency of the sound wave A resonating object absorbs energy from the vibrating object and begins to vibrate too. »Sound waves add to the energy (amplitude) of the object »If a note has the same frequency as a crystal glass, a singer can shatter »Video of Tacoma Narrows bridge How do objects vibrate? What is resonance? What happens two objects with resonance? Examples:

Reverberation A combination of many reflected waves

Music Sound with a pleasing quality, a definite identifiable pitch, and a definite repeated rhythm

Noise Noise has no pleasing quality, no definite identifiable pitch, and/or no definite repeated rhythm

Sonic Booms

METEOR CAUSES SONIC BOOM CNN - Meteor blasts New Zealand with sonic boom - July 8, 1999 Sonic Boom - An explosive sound caused by the shock wave preceding an aircraft traveling at or above the speed of sound

Doppler Effect A change in the frequency & pitch of a sound due to the motion of either the sound source or observer The driver does not hear the pitch change because they are moving with the car. What is the Doppler effect? Does the sound of car horn change for the driver? E E E E E E E O O O O W W W W!!!

Doppler Doppler shift: The person behind the car hears a lower tone than the driver because the car is moving away. The person in front of the car hears a higher tone than the driver because the car is approaching.

TOWARD YOU As the car and its horn move toward you, the sound waves get crammed together (compressed). That makes them a higher-pitched sound. AWAY FROM YOU As the car and the horn move away from you, the sound waves are spread out, further apart (rarefaction). That makes them play a lower note, a lower pitched sound.

More on the Doppler Effect A sound source (car, train, plane) moving toward an observer compresses the sound waves in front of it This causes the observer to hear a higher frequency and pitch A sound source (car, train, plane) moving away from an observer stretches the sound waves behind it This causes the observer to hear a lower frequency and pitch