Vibrations through a medium http://www.youtube.com/watch?v=wvJAgrUBF4w http://www.youtube.com/watch?v=7v0c0Al5X0g 2:00 SOUND Vibrations through a medium

Sound PITCH = The impression about the frequency of a sound All sounds are produced by the vibrations of material objects. PITCH = The impression about the frequency of a sound high pitched – high frequency (ex: piccolo) low pitched – low frequency (ex: fog horn)

Frequency The average frequency range for normal human hearing is between 20 Hz and 20,000 Hz (for younger people; older people lose the higher frequencies). Infrasonic or subsonic = Sounds below 20 Hz Ultrasonic = frequencies above 20,000 Hz http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/ https://www.youtube.com/watch?v=jSkH45nGuM8

Sound in Air Longitudinal or Compression waves travel through air or along springs. These waves travel with areas of compression and rarefaction The medium does not travel from one place to another, but the pulse/energy travels.

Speed of Sound The speed of sound in dry air at 0C is about 330 m/s. For each degree above 0C the speed of sound increases by 0.60 meters per second. Sound travels 15 times faster in steel than air and about 4 times faster in water than air. Any matter will transmit sound, whether it is a solid, liquid or a gas. Sound cannot travel through a vacuum (it is a mechanical wave)

Intensity Intensity is the rate of energy flow through an area. The unit of intensity for sound in the decibel (dB). Sound intensity is objective and is measured by instruments such as an oscilloscope. Loudness is a physiological sensation sensed by the brain. It is subjective but related to sound intensity.

Common Levels of Sound SOURCE OF SOUND LEVEL (dB) Jet Engine, at 30 m 140 Threshold of pain 120 Loud rock music 115 Old subway train 100 Average factory 90 Busy street traffic 70 Normal speech 60 Library 40 Close Whisper 20 Normal breathing 10 Hearing threshold 0

Forced Vibration The vibration of one object cause another object to vibrate. Sounding boards are used to increase the volume (amplitude) of a vibrating object (like a string). STRINGS SOUNDING BOARD

Natural Frequency Everything vibrates, from planets and stars to atoms and almost everything in between. A NATURAL FREQUENCY is one at which minimum energy is required to produce forced vibrations also requires the least amount of energy to continue this vibration

Resonance http://www.youtube.com/watch?v=bDeswHjH1-U Resonance – when the frequency of a forced vibration on an object matches the object’s natural frequency, a dramatic increase in amplitude of the vibrations occurs. For example, a swing, or the hollow box parts of musical instruments are designed to work best with resonance. In order to resonate, an object must be elastic enough to return to its original position and have enough force applied to keep it moving (vibrating) http://www.youtube.com/watch?v=urYWaHfel6g

Interference Sound waves interfere with each other in the same way as all waves. Constructive interference - augmentation Destructive interference - cancellation

The Doppler Effect: Waves from a Moving Source Animation courtesy Dan Russell, Kettering University v=f l so a smaller wavelength means a higher frequency. 12

The Doppler Effect Motion of either the source or the observer of a wave causes the frequency to shift. If the relative motion results in more wave crests reaching the observer per second, the frequency is increased. If the relative motion results in fewer wave crests reaching the observer per second, the frequency is decreased. 13

The Doppler Effect http://www.youtube.com/watch?v=h4OnBYrbCjY 14

Levitation with sound waves http://www.youtube.com/watch?v=odJxJRAxdFU Paint http://www.youtube.com/watch?v=5WKU7gG_ApU Pyro board http://www.youtube.com/watch?v=2awbKQ2DLRE Water standing waves http://www.youtube.com/watch?v=uENITui5_jU Julius https://www.youtube.com/watch?v=pZNNWrA9MZQ https://www.youtube.com/watch?v=OQ9rvkVLlDU