The Energy of WavesThe Energy of WavesChapter 20Chapter 20

Section 1Section 1

The Nature of WavesThe Nature of Waves

pp. 574 - 579pp. 574 - 579

TERMS TO LEARNTERMS TO LEARN

•wave – wave – any disturbance that any disturbance that transmits energy through transmits energy through matter or spacematter or space

•Medium – Medium – a substance a substance through which a wave can through which a wave can traveltravel

TERMS TO LEARNTERMS TO LEARN

•Transverse wave – Transverse wave – a wave in a wave in which particles vibrate with an which particles vibrate with an up and down motionup and down motion

•Longitudinal wave – Longitudinal wave – a wave in a wave in which particles vibrate back and which particles vibrate back and forth along the path that the forth along the path that the wave travelswave travels

WAVES CARRY ENERGYWAVES CARRY ENERGY

• Energy can be Energy can be carried away from its carried away from its source by a wave, source by a wave, but the material but the material through which the through which the wave travels (i.e. wave travels (i.e. water) water) does not does not move with the wave.move with the wave.

• Waves carry energy Waves carry energy but not matterbut not matter..

WAVES CARRY ENERGYWAVES CARRY ENERGY

• Some waves need Some waves need a medium to travel a medium to travel throughthrough..

• These waves are These waves are called called mechanical mechanical waves.waves.

• A medium is a A medium is a substance through substance through which a wave can which a wave can travel.travel.

MECHANICAL WAVESMECHANICAL WAVES• Examples of Examples of

mechanical waves:mechanical waves:– Ocean waves – the Ocean waves – the

medium through medium through which they travel is which they travel is waterwater

– Guitar and cello Guitar and cello strings – the medium strings – the medium through which they through which they travel is airtravel is air

ELECTROMAGNETIC WAVESELECTROMAGNETIC WAVES

• Waves that Waves that DO NOT DO NOT NEED A MEDIUM TO NEED A MEDIUM TO TRAVEL THROUGH TRAVEL THROUGH are called are called electromagnetic electromagnetic waves.waves.

• An example of an An example of an electromagnetic electromagnetic wave is light.wave is light.

ELECTROMAGNETIC WAVESELECTROMAGNETIC WAVES

• Although electromagnetic waves Although electromagnetic waves do do not need a medium to travel not need a medium to travel throughthrough, they may also travel , they may also travel through a medium like air, glass and through a medium like air, glass and water.water.

• Electromagnetic waves (a.k.a. E.M. Electromagnetic waves (a.k.a. E.M. waves) travel fastest through empty waves) travel fastest through empty space ( a vacuum).space ( a vacuum).

CLASSIFICATION OF WAVESCLASSIFICATION OF WAVES

• Waves are classified based on the Waves are classified based on the direction in which the particles direction in which the particles vibrate compared with the direction vibrate compared with the direction in which the waves move.in which the waves move.

• The two main types of waves are The two main types of waves are transverse waves and longitudinal transverse waves and longitudinal waveswaves..

• Longitudinal waves are also called Longitudinal waves are also called compression wavescompression waves..

TRANSVERSE WAVESTRANSVERSE WAVES

• Waves in which the particles vibrate Waves in which the particles vibrate with an up and down motion are with an up and down motion are called called transverse wavestransverse waves..

• The particles in a transverse wave The particles in a transverse wave move move perpendicularperpendicular to the direction to the direction that the wave is traveling.that the wave is traveling.

• Example of a transverse waveExample of a transverse wave: a : a wave moving on a rope.wave moving on a rope.

TRANSVERSE WAVETRANSVERSE WAVEHighest part of wave = crest

Lowest part of wave = trough

TRANSVERSE WAVETRANSVERSE WAVE

LONGITUDINAL WAVELONGITUDINAL WAVE

• A wave in which the particles move back A wave in which the particles move back and forth along the path in which the and forth along the path in which the wave travels is called a wave travels is called a longitudinal longitudinal wavewave..

• CompressionCompression – section of a longitudinal – section of a longitudinal wave where the particles are crowded wave where the particles are crowded togethertogether

• RarefactionRarefaction – section of a longitudinal – section of a longitudinal wave where the particles are less wave where the particles are less crowdedcrowded

LONGITUDINAL WAVELONGITUDINAL WAVE

LONGITUDINAL WAVELONGITUDINAL WAVEcompression

rarefaction

SURFACE WAVESSURFACE WAVES

• When waves occur at or near the When waves occur at or near the boundary between two media, a boundary between two media, a transverse wave and a longitudinal transverse wave and a longitudinal wave can combine to form a wave can combine to form a surface surface wavewave..