Chapter 11Chapter 11

Waves

Waves• wave – a rhythmic disturbance or movement that

transfers energy through matter or space

– examples:

• ocean waves disturb the water and transfer energy through it

• light waves travel through empty space to transfer energy from one place to another

Waves

Waves• wave – a rhythmic disturbance or movement that

transfers energy through matter or space

– examples:

• ocean waves disturb the water and transfer energy through it

• light waves travel through empty space to transfer energy from one place to another

– waves will exist only as long as it has energy to carry

– all waves are created by vibrations

Waves• medium – any material through which an

energy wave is transferred

– the medium for sounds waves is air

– the medium for ocean waves is water

Waves• Mechanical Waves – waves that can only

travel through matter

• Types of Mechanical waves

1. transverse wave - a type of wave where the matter in the medium moves back and forth at right angles to the direction that the wave travels

Waves• Transverse Waves

Waves• Mechanical Waves – waves that can only

travel through matter

• Types of Mechanical waves

1. transverse wave - a type of wave where the matter in the medium moves back and forth at right angles to the direction that the wave travels

• these waves have crests (highest point) and troughs (lowest points)

Waves• Transverse Waves

WavesTypes of Mechanical waves

2.compressional wave - a type of wave where the matter in the medium moves back and forth in the same direction that the wave travels

– similar in movement to the compression and expansion of a spring

Waves2. compressional wave - a type of wave where the

matter in the medium moves back and forth in the same direction that the wave travels

– similar in movement to the compression and expansion of a spring

– example: sound waves occur when air molecules are pushed together when a surface is hit and that sound is carried through compressions and expansions of the wave through air

– causes the eardrum to vibrate when it reaches the eardrum

Waves• Compressional Wave

WavesParts of a Transverse Wave

• crest – the highest points of the wave

• trough – the lowest points of the wave

WavesParts of a Compressional Wave

• compression – the denser (or more compressed) region of the wave

– example: where the coils are close together

• rarefaction – less dense (or more stretched) region of the wave

– example: where the coils are more spread out

Waves• Compressional Wave

WavesCommon Parts of Waves

• wavelength – distance between one point on a wave and the nearest point just like it

– measured in meters (m)

– represented with the Greek letter lambda λ

WavesCommon Parts of Waves

• frequency (f) – the number of wavelengths that pass a fixed point each second

– measured in hertz (Hz = 1/s)

Waves• Wave Velocity (v) – describes how fast a

wave is traveling

– measured in meters per second (m/s)

– example: v = 300,000,000 m/s for most electromagnetic waves in a vacuum

WavesCalculating Velocities of Waves

• the speed of a wave depends on the medium through which it is traveling

• sound waves usually travel faster in liquids and solids than they do in gases

• light waves and other electromagnetic waves usually travel faster in gases or a vacuum than they do in solids and liquids

Waves• Formula for calculating the velocity of a wave:

– v: velocity (in m/s)

– : wavelength (in m)

– f: frequency (in Hz or 1/s)

v = f

Waves

• What is the speed of a wave with a wavelength of 2 m and a frequency of 3 Hz?

v = f

Waves

• A wave is traveling at a velocity of 12 m/s and its wavelength is 3 m. Calculate the wave frequency.

v = f

Waves• amplitude – a measure of the energy carried

by a wave

– Transverse Waves

• the taller the wave, the more energy it has

• the shorter the wave, the less energy it has

Waves• amplitude – a measure of the energy carried

by a wave

– Compressional Waves

• the more dense the wave, the more energy it has

• the less dense the wave, the less energy it has

Waves• Compressional Waves