# Sound and Wave Interactions. Sound “If a tree falls in a forest …?” What is sound? –Longitudinal wave, particles transfer energy –Mechanical wave, must.

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Sound and Wave Interactions

Sound “If a tree falls in a forest …?” What is sound? –Longitudinal wave, particles transfer energy –Mechanical wave, must have a medium Bell in a vacuum

Sound and Amplitude Amplitude: effects the loudness (volume) of sound –Decibel (db) measures volume Direction of wave travel

Sound and frequency Frequency: determines “pitch” you hear –How “high” or “low” the sound seems –Gizmo on frequencyGizmo on frequency –Ultrasound: above human hearing Dog whistles –Infrasound: below human hearing whales

Sound and Frequency –Resonance: natural frequency of an object causes it to vibrate Glass of water Speaker/strobe Bridge Collapse –Doppler Effect: sound waves change pitch as they moveDoppler Effect: Sound waves pushed together in front of moving object (higher frequency) –sound of Dopplersound of Doppler Doppler Radar Wave interactions video

Speed of Sound The speed of sound depends on 3 things 1.Elasticity: ability for medium to “bounce back” More elastic means faster sounds –Solids are most elastic, liquids less, and gases not very elastic at all 2.Density: how many particles are in a given space [HOWEVER, more density means slower sounds within the same phase of matter (more dense solids will be slower than less dense solids, etc.)] 3.Temperature: higher kinetic energy (higher temps) = faster sound travel. –Speed of Sound videoSpeed of Sound video

What happens when waves meet? Reflections The bouncing back of wave as it hits another object Law of reflection: “angle in = angle out” –Echoes –Echolocation »Sonar DVD

Diffraction –Waves bend and spread out around an object Example: sound carries around a corner or over a hill (see diagram) from where it was made

Interference When two waves meet: –Constructive interference: a bigger wave is produced as the crests meet –Destructive interference: waves of equal amplitude meet with the crest of one and the trough of the other to cancel each other out Active art on interferencective art on interference Gizmo on Sound Interference

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