Resonance: occurs when an object absorbs energy from vibrations that are at its natural frequencies If one tuning fork is struck, its vibrations will cause the second one to start vibrating if they both resonate at the same frequency. Tacoma Bridge Collapse:

Chapter 11: Sound Sound waves: Compressional waves that require some form of matter (solid, liquid or gas) for transmission Outer ear gathers sound waves Middle ear amplifies sound waves Inner ear converts vibrations into nerve impulses

The speed of sound Through which state of matter will sound travel the fastest? The slowest? Because sound is a compressional wave, it travels fastest through solids because the particles are close together and can push against each other easily. In a gas, the particles are very far apart and sound travels more slowly. Sound does not travel at all in a vacuum (outer space).

Air Cork Water Brick Aluminum Air Cork Water Brick Aluminum Slow wave speed Fast wave speed Arrange materials in order of increasing sound transmission rates

Some numerical values:

Sound intensity Recall that the amplitude (intensity) of a compressional wave depends upon how tightly packed the compressions are. Compression Rarefaction

The greater the intensity of a sound, the more energy is being transmitted by the wave. The Decibel Scale: measures the intensity of a sound. Units are decibels (dB)

In which direction was the xylophone played? Frequency and Pitch The shorter the bar, the higher the pitch. Shorter bar = shorter wavelength = higher frequency The higher the frequency, the higher the pitch

Doppler Effect: a change in pitch due to motion of the source of the wave or of the observer. Source moving toward observer. Sound wave compressed = higher frequency Source moving away. Sound wave expanded = lower frequency Siren emits at a constant 300 Hz

Which way is the sound travelling? Toward the observer or away? Away Toward