SOUND intro

Remember: Waves transport ENERGY

Sound Waves Sound Waves are Compressional waves. The vibrations of the molecules are parallel to the direction of the wave. Produced by the compressions and rarefaction of matter.

Sound Wave Propagation Sound is produced by a vibrating object. As one individual particle is disturbed, it transmits the disturbance to the next interconnected particle. This disturbance continues to be passed on to the next particle. The result is that energy is transported without the actual transport of matter. Clip

How We Hear

When a sound wave reaches the ear, a series of high and low pressure regions hit the eardrum. The arrival of a compression or high pressure region pushes the eardrum inward; the arrival of a low pressure regions serves to “pull” the eardrum outward. The continuous arrival of high and low pressure regions sets the eardrum into motion. Video Clip Eardrum

Frequency and Pitch The frequency of a sound wave determines the pitch. Pitch is the highness or lowness of a sound. The higher the frequency…the higher the pitch. Clip

Low Pitch High Pitch Sound waves below 20 Hz are called infrasonic. Sounds waves above 20,000 Hz are called ultrasonic. Range of Human Hearing is from about 20 Hz –20,000 Hz

Bioacoustics is a branch of science concerned with the production of sound and its effects on living systems. Animals that generate “infrasound” include elephants, whales, alligators, hippos, rhinos, giraffe, lions, tigers and several birds. (whale) Animals that generate “ultrasound” include Dolphins, bats, many birds and insects.

Echolocation Bats send out sound waves using their mouth or nose. When the sound hits an object an echo comes back. They can detect the distance between themselves and the object   They can identify an object by the sound of the echo. They can even tell the size, shape and texture of  a tiny insect from its echo.   Most bats use echolocation to navigate in the dark and find food. VIDEO Echolocation

Animal Communication With Sound

Sonar

Speed of Sound Speed depends upon how fast one particle can transfer its motion to another particle. Remember: Sound waves are mechanical waves. Speed of sound depends on the medium Temperature Why?

What is the Speed of Sound? Video Clip

Loudness Depends on the amplitude. Larger A means more pressure. Remember: A is measure of the amount of energy in the wave. Sound level is measured in Decibels.

Common Sounds in Decibels Decibel Level Listener's Perception Whisper 10 Barely Audible Quiet Conversation 30 Faintly Heard Average Office 50 Moderate Level Summer Nocturnal Insects 60 Noisy Office 70 Loud Average Street Traffic 85 Very Loud Jackhammer 100 Extremely Loud Jet Aircraft Taking Off 120 Physical Pain

All sound consists of a waves. If you add 2 waves together that are going in the same direction, and if those waves are in phase--that is, the peaks and valleys of the waves line up--then the amplitude or height of the waves will double. Constructive Interference

Destructive Interference If you add 2 waves that are going in the same direction, and if those waves are completely out of phase--that is, the peaks of one line up with the valleys of the other--then the amplitude or height of the waves cancel each other out. Waves out of phase will cancel each other Destructive Interference

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Echo vs. Reverberation Sound waves can be reflected A reverberation is perceived when the reflected sound wave reaches your ear in less than 0.1 second after the original sound wave.

Tacoma Narrows Bridge Collapse (Nov.7th 1940) Galloping Gertie On a day of rather high winds, Gertie took on a 30-hertz transverse vibration (like sending waves down a rope by moving the end up and down) with an amplitude of 1½ feet! It later took on a twisting motion of about 14 hertz and quickly tore itself in two.

Doppler Effect Variation in the perceived pitch of a sound due to a moving sound source. “bunches up “ in front of the source Spreads out behind the source Website

Website Web Site

Sonic Boom a "sonic boom" is the sudden onset and release of pressure after the buildup by the shock wave Example

Click on the Picture

This picture shows a sonic boom created by the THRUST SSC team car as it broke the land speed record (and also broke the sound barrier on land).