Sound Wave Interactions

Sound … 1. Is a form of energy produced & transmitted by vibrating matter 2. Travels in waves 3. It needs a medium to travel Any SOLID, LIQUID OR GAS

Sound is produced by vibrations A vibration is a complete back and forth motion of an object

More on Compressional Waves Animation of above compressional wave: http://www.passmyexams.co.uk/GCSE/physics/basic-waves-theory.html

Sounds from a Stereo Speaker Every time the cone vibrates, compressions and rarefactions are formed. As these compressions and rarefactions travel away from the speaker, sound is transmitted through the air

Compressions vs. Rarefactions Speaker moves forward Creates these high density & pressure regions Rarefactions Speaker moves backward Creates these low density and pressure regions

Amplitude of Compressional Waves In higher amplitude of a compressional/longitudinal wave, the particles of a compression are closer, and particles in the rarefaction are farther apart. In lower amplitude, the particles in compression are farther apart, and rarefaction particles are closer together

Common Sounds and their Loudness

Riddle Me This If a tree falls in the woods and there is no one around to hear it, does it still make a sound? YES!! Creating a sound is different than detecting sound! Sounds need a medium to travel through A medium is any substance through which a wave can travel (water, sand, ground, air)

Sound waves travel on a MEDIUM: Any SOLID, LIQUID OR GAS Sound travels by pushing the particles of a substance. The particles push into the particles next to them, and then return to their original position. And the sound continues to travel in this form until it reaches your ear!

Speed of sound depend on the. - temperature of the medium Speed of sound depend on the - temperature of the medium - substance of the medium - state of matter ?

Temperature The particles in cool materials move slower than particles in warmer materials

Which state of substance would sound travel through faster? WHY?

Mediums: Sound travels through a solid faster, than through a liquid, which is faster, than through a gas. Our ears are custom to hear sound through a gas…

Pitch A measure of how high or low a sound is Pitch depends on the frequency of a sound wave For example, Low pitch Low frequency Longer wavelength High pitch High frequency Shorter wavelength

The average human ear can detect sounds that have frequencies between 20Hz and 20,000 Hz

Sounds with frequencies that are higher than 20,000 Hz are called Ultrasonic. Sounds with frequencies that are lower than 20 Hz are called Infrasonic. ultrasonic waves infrasonic waves

Reflection The bouncing back of a wave after it hits a barrier called an echo (visual concepts = echo) Sounds reflect best off solid, smooth surfaces

Reflection Echolocation Ultrasonography Process of using reflected sound waves to find objects (see next slide) Beluga whales, bats, dolphins use echolocation to find food and detect objects in their paths Uses echoes to “see” inside a patients body without performing surgery Used to examine kidneys, gallbladders, and the development of unborn babies Safer than x-rays b/c sound waves are less harmful to human tissue Visual Concepts = Sonar

Humans use sonar to locate or map objects An instrument that uses reflected sound waves to find underwater objects For example, Humans use sonar to locate or map objects Animals use sonar or echo location to find their prey; these sounds have such a high pitch or frequency that the human ear cannot hear

Interference The result of two or more waves overlapping Louder sounds occur during constructive interference (means high amplitude = C + C) Dead spots occur during destructive interference (means no amplitude, wave is at rest position = C + R) Compression + Compression = CI = LOUD Compression + Rarefaction = DI = SOFT or DEAD SPOT

Supersonic (breaking sound barrier) When a wave source catches up and passes the outgoing waves of energy. Sound barrier Click for video example

Interference Sound Barrier Sonic Boom As a jet plane accelerates to the speed ofsound, the sound waves in front of the jet compress closer (high frequency) The explosive sound you hear when a shock wave reaches your ears Visual Concepts = sonic boom

Doppler Effect The apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound.

The Doppler Effect The Doppler effect causes the changing pitch of a siren. When a firetruck approaches, the pitch sounds higher than normal because the sound wave crests arrive more frequently. When the firetruck passes and moves away, you hear a drop in pitch because the wave crests are arriving less frequently. Note: The change in loudness is not the Doppler Effect! It is the shift in frequency!

The Doppler Effect Police use the Doppler effect of radar waves to measure the speeds of cars on the highway. Radar waves are electromagnetic waves. Police bounce them off moving cars. A computer built into the radar system compares the frequency of the radar with the frequency of the reflected waves to find the speed of the car.