Waves and Sound

A disturbance or oscillation that travels through space and matter, accompanied by a transfer of energy. Big Idea 6: Waves can transfer energy and momentum from one location to another without the permanent transfer of mass and serve as a mathematical model for the description of other phenomena. Wave

Parts of the wave

Essential Knowledge 6.B.1: For a periodic wave, the period is the repeat time of the wave. The frequency is the number of repetitions of the wave per unit time. Essential Knowledge 6.B.4: For a periodic wave, wavelength is the ratio of speed over frequency. Essential Knowledge 6.A.3: The amplitude is the maximum displacement of a wave from its equilibrium value. Definitions

Frequency and speed of a wave

Wave in a string

Essential Knowledge 6.A.1: Waves can propagate via different oscillation modes such as transverse and longitudinal. a. Mechanical waves can be either transverse or longitudinal. Examples should include waves on a stretched string and sound waves. b. Electromagnetic waves are transverse waves. Types of waves

Transverse wave A transverse wave is one in which the disturbance is perpendicular to the direction of travel of the wave. Examples: Light wave, waves on a guitar string.

Longitudinal wave Longitudinal wave is one in which the disturbance is parallel to the line of travel of the wave. Example: Sound wave in air is a longitudinal wave.

Superposition principle When two waves interact, the resulting wave function is the sum of the two individual wave functions. This phenomena is generally described as interference. When crest and crest or trough and trough meet, they add up creating a bigger wave. This is constructive interference. When a crest and a trough meet, they cancel each other. This destructive interference.

Essential Knowledge 6.C.1: When two waves cross, they travel through each other; they do not bounce off each other. Where the waves overlap, the resulting displacement can be determined by adding the displacements of the two waves. This is called superposition. Superposition

12 Constructive Interference  They will ADD together to produce a greater amplitude.

13 Destructive Interference  This time when they add together they will produce a smaller amplitude.

Standing Waves  Amplitude is zero at fixed ends  Nodes (other places with zero amplitude)  Anti-nodes (places with maximum amplitude) …a wave in which the amplitude at a given location does not vary with time. Standing Wave Features:

Standing Wave: Both Ends Fixed

Standing Wave: One End Fixed, One End Free

Longitudinal Needs a medium Can not be polarized. The speed of sound in air is affected by the air temperature as given in the following formula: v sound = m/s + (T C )(0.6 m/s∙  C) Sound

Doppler effect The change in frequency heard by an observer whenever there is relative motion between the source and the observer. Essential Knowledge 6.B.5: The observed frequency of a wave depends on the relative motion of source and observer.

Resonance is the tendency of a system to oscillate with greater amplitude at some frequencies than at others. Happens in an air column whenever a standing wave is formed. Resonance

open at one end and closed at the other resonance will occur whenever there is a node at the closed end and an antinode at the open end Closed-pipe Resonator

open-pipe air column is open at both ends resonance will occur whenever there is an antinode at both open ends Open-pipe Resonator

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