What is a sound wave? Mechanical wave – longitudinal *A vibration *Particles of medium are disturbed *Causes a wave causes Most common medium is air Can travel through solids and liquids

Sound Interactions Reflection – Echo - when a sound wave reflects off a surface. Harder and smoother the surface the stronger the reflection. Diffraction – Through openings (doorways) – Around corners Interference – Can be: Destructive – sound will be fainter Constructive – sound will be louder

Speed of Sound (SOS) 343 m/s – at room temperature through air Depends on medium sound is traveling through – 3 characteristics of the medium affect SOS: 1. Elasticity 2. Density 3. Temperature

Elasticity The ability of a medium to bounce back after being disturbed. More elastic medium – the particles bounce back faster – sound travels faster. Less elastic medium – the particles bounce back slowly – sound travels slower. From faster to slower: solids > liquids > gases

Density Sound travels more slowly in denser mediums Due to particles not moving as quickly back to rest position in denser materials (too crowded).

Temperature Sound travels more slowly at lower temperatures than higher temperatures. Because particles move slower in lower temperatures.

SOS final thoughts The faster the particles of the medium can return to rest position – the faster sound will move through medium. – More elastic – faster (bounce back quicker) – Less dense – faster (not as crowded) – Higher temp – faster (particles naturally move faster) First person to break sound barrier (go faster than sound) – Chuck Yeager – Flew at higher altitude b/c lower temp = lower SOS

Properties of sound Loudness – depends on amount of energy used to create sound (amplitude of wave). Pitch – depends on frequency of wave.

Loudness Depends on 2 things: – The amount of energy it takes to make the sound. – The distance from the source of the sound. Decibel (dB) – unit for loudness of sound Intensity – The amount of energy a sound wave carries over a certain amount time in a particular area.

Pitch How high or low the sound seems High pitch – high frequency Low pitch – low frequency Ultrasound – sound waves with freq. above normal human hearing. (Usually above 20,000 Hz) Infrasound – Below human range of hearing (usually under 20 Hz)

The Doppler Effect The change in frequency (pitch) as a source of sound MOVES in relation to the observer. – Pitch increases as source moves toward observer. – Pitch decreases as source moves away. Think of a siren approaching then passing by. It sounds different. Can happen with light waves also.