Sound Waves Can you hear me now?

Wave Review Sound is a Longitudinal Wave- it moves back and forth like a spring. Sound is a Mechanical Wave- it needs a medium, like water or air to travel through. Sound is a Pressure Wave- it creates a difference in pressure in the medium.

Tuning Forks Tuning Forks create sound by vibrating tines that push air away, creating sound waves.

Pressure Waves As air is pushed by the tines, it creates areas of compression (higher pressure). In between areas of compression are areas of rarefaction (lower pressure). This creates the “high” part of the wave, and the “low” part.

Density of Air Molecules

Pressure of a Sound Wave

Now do you hear me? When the high/low pressure wave hits the eardrum, it causes it to vibrate, and your brain translates these into sounds, letting you “hear”.

Wave Terminology Review How fast the tuning fork tines are moving back and forth is the frequency (f) that the sound wave is being created at. Frequency (f) = # of vibrations / second Frequency (f)- Hertz (Hz)

Wave Terminology Review The distance between high pressure areas of the sound wave is the wave’s Period (T)

Getting Musical The sensation (what we “hear”) of a sound wave’s frequency is referred to as it’s pitch. A higher frequency (faster vibrating tuning fork), creates a higher pitch- a treble note. Lower frequency (slower vibrating tuning fork), creates a lower pitch- a bass note.

Octaves Any two notes (pitch) whose frequencies are a 2:1 ratio (one is twice as fast as the other), are separated by an ocatve. Putting notes together with specific mathematical ratios creates scales, chords, and harmonies.

Breaking down the music scale IntervalFrequency Ratio Examples Octave2:1 512 Hz and 256 Hz Third5:4 320 Hz and 256 Hz Fourth4:3 342 Hz and 256 Hz Fifth3:2 384 Hz and 256 Hz

Characteristics of Sound Waves Because of the nature of air molecules, sound waves travel outward in every direction at once. The high/low pressure waves don’t just go in straight lines (imagine a rock being dropped in a pond).

Decibels The larger the amplitude (amount of high and low pressure created) of the sound wave, the more energy it carries. Greater energy creates a louder sound. Sound intensity is measured in Decibels (dB). Clapping your hands harder requires more energy, the sound wave carries more energy, the sound is louder.

SourceIntensity Level # of Times Greater Than TOH Threshold of Hearing (TOH)1* W/m 2 0 dB10 0 Rustling Leaves1* W/m 2 10 dB10 1 Whisper1* W/m 2 20 dB10 2 Normal Conversation1*10 -6 W/m 2 60 dB10 6 Busy Street Traffic1*10 -5 W/m 2 70 dB10 7 Vacuum Cleaner1*10 -4 W/m 2 80 dB10 8 Large Orchestra6.3*10 -3 W/m 2 98 dB Walkman at Maximum Level1*10 -2 W/m dB10 Front Rows of Rock Concert1*10 -1 W/m dB10 11 Threshold of Pain1*10 1 W/m dB10 13 Military Jet Takeoff1*10 2 W/m dB10 14 Instant Perforation of Eardrum1*10 4 W/m dB10 16

Sound Wave Intensity Sound waves carry a certain amount of power (Watts), and they move outward in a circle from their source. Putting these two together gives:

Sound Wave Intensity What is the intensity of the sound waves produced by a trumpet at a distance of 3.2m when the power output of the trumpet is 0.20 W? Assume that the sound waves are spherical.

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