Sound Waves

Sound is a compressional or longitudinal wave The “wiggle” (compression) is in the same direction as the wave travels

What it looks like... Instead of crests and troughs, as we see in transverse waves, we have compressions and rarefactions

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Frequency All waves have a frequency The frequency of a sound determines the pitch of the sound – High frequency, high pitch Standard human hearing range is from 20 Hz to 20,000 Hz

Amplitude Amplitude of a transverse wave relates to how tall the wave is Amplitude in a compressional wave relates to how much is compressed The amplitude of a sound determines its intensity, or loudness

Doppler Effect The Doppler Effect is an apparent change in the pitch of a sound caused by the motion of the sound generator Emergency vehicle sirens, and car tires, sound higher as they approach and lower as they pass The Doppler Ball will do the same thing!

The apparent change in pitch is caused by a change in the distances between waves As a wave is created, it moves away from the source If the source move in the same direction as the wave, chasing it, the next wave will be closer to the previous wave, creating a higher pitch

As the sound source moves away, it creates a larger distance between the first and second wave, creating a lower pitch Internet demo

Natural Frequency When many objects fall or get hit, they ring – like the tuning fork The specific frequency, or frequencies, an object rings at is its natural frequency Using your finger to make a water glass ring is showing its natural frequency

Resonance When another sound or vibration continues to hit an object, it can cause the other object to vibrate If the frequency of the sound matches the natural frequency of the other object, it can cause resonance This means that the object will vibrate, and can increase vibrations Resonance was how the Myth Busters were able to break the wine glass