When a vibration or an oscillation repeats itself, back and forth, over the same path, the motion is called periodic. Examples: swing, vibrating spring,

When a vibration or an oscillation repeats itself, back and forth, over the same path, the motion is called periodic.

Examples: swing, vibrating spring, grandfather clock, different types of waves

ALL Waves carry energy

Periodic Motion

Different types of waves around us: Ocean waves:

Greeting or cheering waves:

Shaking a rope waves:

Compressing a slinky waves: Electromagnetic waves

(radio; TV; X-rays; microwaves)

Mass on a spring; Circular motion and pendulum waves:

http://positron.ps.uci.edu/~dkirkby/music/html/demos/SimpleHarmonicMotion/index.html http://www.youtube.com/watch?v=eZm_-2O8ovI&annotation_id=annotation_120510&feature=iv&src_vid=7_AiV12XBbI

A sound wave is produced by a vibrating object. As a sound source (guitar string; tuning fork, etc.) vibrates, it sets surrounding air molecules into vibrational motion.

eardrumGuitar stringTuning fork

…and last but not least: Sound waves

Sound waves in 1 and 2 dimensions:

http://positron.ps.uci.edu/~dkirkby/music/html/demos/PlaneWave/SoundGraph.html

Sound Waves

Sinusoidal Nature of WavesAll types of waves could be described using trigonometric functions:

Where A is the amplitude; is the angular frequency (in radians per seconds) and is the phase shift

)sin( tAy

)(sin CxBAy

periodf

T

frequencyf

;21

;2

Practice with computer simulated sound: Datastudio software

Sound in everyday lifePitch: related to frequency.

Audible range: about 20 Hz to 20,000 Hz;

Ultrasound: above 20,000 Hz;

Infrasound: below 20 HzLoudness: related to amplitude of the sound waveThere are two different ways to measure loudness:1. Using the subjective sensation of a human being;2. Using the physically measurable quantity “intensity” of sound;