Waves

Waves

1Part 1: Kinds of Waves

What is a Wave?

A wave is a disturbance in space/time that moves energy in a straight line from one place to another.

When waves move through matter, we call that matter the waves medium.

A medium can be a solid, liquid, or a gas.

Light waves can move through empty space and do not need any medium at all.

When energy waves move through a medium, the medium is disturbed, but it stays in the same place as the wave travels through it.

In the ocean, when a wave passes, the water molecules only move in small circles!

Types of Waves : TransverseA wave where the medium moves at right angles to the direction of the wave is called a transverse wave.

Ocean waves and light waves are both transverse waves.Energy moves in this direction Medium moves in this directionParts of a Transverse WaveThe crest is the highest point of a transverse wave, and the trough is its lowest point.

One wavelength includes one complete crest plus one complete trough.

The amplitude of a transverse wave is the distance from the normal to a crest or from the normal to a trough.

The more energy a wave has, the greater its amplitude. Parts of a Transverse WaveWavelengthWavelengthAmplitudeAmplitudeTroughTroughNormalCrestCrestTypes of Waves: LongitudinalA longitudinal wave makes the medium move parallel to the direction in which the wave is traveling.

Sound travels in longitudinal waves.

Unlike some transverse waves that can travel through empty space, longitudinal waves MUST have a medium to travel through.

This is why there is no sound in outer space.

Parts of a Longitudinal WaveThe part of a longitudinal wave where the particles of the medium are close together is a compression.

The part of a longitudinal wave where the particles of the medium are far apart is a rarefaction.

One wavelength includes one complete compression plus one complete rarefaction.

Parts of a Longitudinal WaveCompressionsRarefactionsWavelengthWavelengthHow many complete wavelengths are shown here? 4Part 2: Wave Properties (Characteristics)

Wave PropertiesWhen you talk about a big wave at the beach, you are describing the waves amplitude.

If you describe how many waves pass you in a given time, you are describing the frequency of the waves.

For transverse waves, the distance from crest to crest or trough to trough is a wavelength.

For a longitudinal wave, a wavelength is the distance between compressions or between rarefactions. It is measured in meters.

Wave Properties

Wave AmplitudeIf you are looking at transverse waves (think ocean waves), amplitude is the vertical (up and down) distance from the normal to the crest or trough.

As you increase a waves energy, its amplitude also increases.

In other words, high energy waves have high amplitude, and low energy waves have low amplitude.

Wave Amplitude

Wave FrequencyThe frequency of a wave is the number of waves that pass by a place in a certain length of time.

The most common unit for frequency is the Hertz (Hz), which means waves per second. Wave FrequencyNotice that both waves below have the same amplitude, and therefore the same amount of energy.

Wave SpeedWave speed measures how fast the wave is moving toward you.

The metric unit most often used to measure wave speed is meters second.

Wave speed = frequency x wavelength

In the open ocean, tsunami waves can travel at speeds of up to 550 miles per hour (890 km/hour)as fast as a jet plane! Math Problems with WavesWave Speed, Frequency, and are related by the formula:speed = frequency x wavelength

Solve these. Show your work in KFCA form.If a waves speed is 200 m/s and its frequency is 650 Hz, what is its wavelength?

A wave traveling at a speed of 3500 m/s has a wavelength of 14 meters. What is its frequency?

A wave has a frequency of 250 Hz and a wavelength of 0.3 m. What is its speed?

A sound traveling at 340 m/s has a frequency of 8500 Hz. What is its wavelength?

Answers to ProblemsKFCAs = 200 m/secf = 650 Hz = ? = s f = 200 m/sec 650 waves/sec = 0.31 m/waves = 3500 m/secf = = 14 m/wavef = s f = 3500 m/sec 14 m/wave

f = 250 waves/sec or 250 Hzs = ?f = 250 Hz = 0.3 m/waves = f s = (250 waves/sec) x (0.3 m/wave)s = 75 m/secs = 340 m/secf = 8500 Hz = ? = s f = 340 m/sec 8500wave/sec = 0.04 m/wavePart 3: Wave Interactions

Wave Interactions: Energy and ChangeWhen a wave runs into another wave or into an object, the waves energy changes.

The change in the waves energy makes the waves properties change too.

Wave properties include: speedAmplitude Wavelengthfrequency

When an ocean wave hits the shore, its amplitude, speed, or wavelength might change.Wave Interactions: Energy and ChangeOther changes that might happen are a change in the waves direction, or it might break apart and then re-form as a group of small waves.

Wave interactions affect ALL kinds of waves: ocean waves light wavessound waves!Kinds of wave interactions include: reflectionRefractionDiffractioninterferenceWave Interactions: Reflection Reflection happens when a wave hits a surface and bounces off.

The angle of the incoming (incident) wave equals the angle of the outgoing (reflected) wave.

This is the Law of Reflection

Wave Interactions: RefractionRefraction is the bending of a wave because it changes speed when it goes through different media.

Sounds travel fastest in solids, slower in liquids, and slowest in gases like air.

Sound cannot travel at all through a vacuum like space.

Light travels fastest in a vacuum (outer space) slower through a gas, even slower through a liquid, and slowest through a solid like glass.Wave Interactions: RefractionWaves change speed when they pass from one medium to another.

The green fish seems to be in a different place because the light waves bend when they change from water to air.

Wave Interactions: DiffractionThe bending of a wave as it touches the edge of a barrier is called diffraction.

When waves are diffracted at the edge of a barrier, speed and direction may change, but wavelength and frequency might not change.

Diffraction allows you to hear sounds around corners.

Diffraction glasses split white light into rainbow colors.

Wave Interactions: DiffractionIncoming wave crests

outgoing wave crestsWave Interactions: InterferenceThe effect of two or more waves interacting with each other is called interference.There are two kinds of interference: constructive and destructive.When the crests and troughs of the interacting waves are in the same place at the same time, the result is a larger wave. This is constructive interference. Tsunamis are caused by constructive interference ! ! !Wave Interactions: Interference When the crest of one wave meets the trough of another wave, the result is a smaller wave. This is destructive interference.

In poorly built auditorium, destructive interference between sound waves makes it hard to hear whats happening on stage.