WavesWaves

The Nature of The Nature of WavesWaves

What is in a wave?What is in a wave?

•A A wavewave is a repeating is a repeating disturbance or movement that disturbance or movement that transfers energy through matter transfers energy through matter or space.or space.

•For example, during earthquakes, For example, during earthquakes, energy is transferred in powerful energy is transferred in powerful waves that travel through Earth. waves that travel through Earth.

Wave and EnergyWave and Energy

•A pebble falls into a pool A pebble falls into a pool of water and ripples form. of water and ripples form.

•Because it is moving, the Because it is moving, the falling pebble has falling pebble has energy. energy.

•As it splashes into the pool, As it splashes into the pool, the pebble transfers some the pebble transfers some of its energy to nearby of its energy to nearby water molecules, causing water molecules, causing them to move.them to move.

•What you see is energy What you see is energy traveling in the form of a traveling in the form of a wave on the surface of the wave on the surface of the water. water.

•RaftRaft

• The waves don’t even carry The waves don’t even carry the water along with them. the water along with them.

•Only the energy carried by Only the energy carried by the waves moves forward. the waves moves forward.

•All waves have this propertyAll waves have this property•They carry energy without They carry energy without transporting matter from place transporting matter from place to place. to place.

Making WavesMaking Waves•A wave will travel only as A wave will travel only as

long as it has energy to carry. long as it has energy to carry.

•Anything moving up and Anything moving up and down or back and forth in down or back and forth in rhythm is vibrating. rhythm is vibrating.

•All waves are produced by All waves are produced by vibrating mattervibrating matter

Mechanical WavesMechanical Waves•Some wave require matter to Some wave require matter to

transfer the energy.transfer the energy.

•The matter the waves travel The matter the waves travel through is called a through is called a mediummedium. .

•The medium can be a solid, a The medium can be a solid, a liquid, a gas, or a liquid, a gas, or a combination of these. combination of these.

•The two types of The two types of mechanical waves are mechanical waves are transversetransverse waves and waves and compressionalcompressional waves. waves.

Transverse WaveTransverse Wave• In a In a transverse transverse

wavewave, matter in , matter in the medium moves the medium moves back and forth at back and forth at right angles to the right angles to the direction that the direction that the wave travels. wave travels.

• For example, a For example, a water wave travels water wave travels horizontally as the horizontally as the water moves water moves vertically up and vertically up and down. down.

Compressional Waves Compressional Waves

•In a In a compressional wavecompressional wave, , matter in the medium moves matter in the medium moves back and forth along the same back and forth along the same direction that the wave travels.direction that the wave travels.

•The wave carries energy, but The wave carries energy, but not matter, forward along the not matter, forward along the spring.spring.

•Compressional waves also Compressional waves also are called are called longitudinallongitudinal waves waves

•Sound creates Sound creates compressional waves.compressional waves.

Deep Water WavesDeep Water Waves

•A water wave causes water to A water wave causes water to move back and forth, as well move back and forth, as well as up and down. as up and down.

•This motion causes both This motion causes both transverse and compressional transverse and compressional waveswaves

Seismic WavesSeismic Waves• Forces in Earth’s crust can cause Forces in Earth’s crust can cause

regions of the crust to shift, bend, regions of the crust to shift, bend, or even break.or even break.

• The breaking The breaking crust vibrates, crust vibrates, creating seismic creating seismic waves that waves that carry energy carry energy outward. outward.

•Seismic wavesSeismic waves are a are a combination of compressional combination of compressional and transverse waves. and transverse waves.

•They can travel through Earth They can travel through Earth and along Earth’s surface.and along Earth’s surface.

Wave Wave PropertiesProperties

The Parts of a WaveThe Parts of a Wave•Transverse wavesTransverse waves and and

compressional wavescompressional waves have have different characteristics: crests different characteristics: crests and trough, compressions and and trough, compressions and rarefactions.rarefactions.

•They also have similar They also have similar properties: wavelength, properties: wavelength, frequency, period, amplitude, frequency, period, amplitude, and wave speed.and wave speed.

The Parts of a Transverse The Parts of a Transverse WaveWave

•A transverse wave has A transverse wave has alternating high points, alternating high points, crestscrests, , and low points, and low points, troughstroughs..

Rest Rest position is position is also called also called equilibriumequilibrium..

Wavelength of Transverse Wavelength of Transverse WaveWave

•A A wavelengthwavelength, , ,, is the distance is the distance between one point on a wave between one point on a wave and the nearest point just like it.and the nearest point just like it.

• Wavelength is Wavelength is the distance the distance from crest to from crest to crest or crest or trough to trough to trough.trough.

The Parts of a Compressional The Parts of a Compressional WaveWave

•A compressional wave has A compressional wave has regions where the particles are regions where the particles are close together, close together, compressionscompressions..

•And regions And regions where the where the particles are particles are further apart, further apart, rarefactionsrarefactions..

The wavelength of a The wavelength of a Compressional WaveCompressional Wave

•A wavelength is the distance A wavelength is the distance between two neighboring between two neighboring compressions or two neighboring compressions or two neighboring rarefactions.rarefactions.

AmplitudeAmplitude

•AmplitudeAmplitude is related to the is related to the energy carried by a wave.energy carried by a wave.

•The greater the wave’s The greater the wave’s amplitude is, the more energy amplitude is, the more energy the wave carries.the wave carries.

Amplitude of a Transverse Amplitude of a Transverse WaveWave•The The amplitudeamplitude is the distance is the distance

from the crest or trough of the from the crest or trough of the wave to the rest position of the wave to the rest position of the medium.medium.

The Amplitude of a The Amplitude of a Compressional WaveCompressional Wave

•The amplitude of a compressional The amplitude of a compressional wave is related to how tightly the wave is related to how tightly the medium is pushed together at medium is pushed together at the compressions.the compressions.

•The denser the medium is at the The denser the medium is at the compressions, the larger its compressions, the larger its amplitude is and the more energy amplitude is and the more energy the wave carries.the wave carries.

Frequency, fFrequency, f•The number of wavelengths that The number of wavelengths that

pass a fixed point each second.pass a fixed point each second.

•The rate of vibrationThe rate of vibration

•Find the frequency of a Find the frequency of a transverse wave by counting the transverse wave by counting the number of crests or troughs that number of crests or troughs that pass by a point each second.pass by a point each second.

•Expressed in Expressed in HertzHertz (Hz). (Hz).

Period, TPeriod, T

•The amount of time it takes The amount of time it takes one wavelength to pass a one wavelength to pass a point.point.

•As the frequency of a wave As the frequency of a wave increases, the period increases, the period decreases.decreases.

•Units of seconds, s.Units of seconds, s.

Frequency & PeriodFrequency & Period

•The frequency, f, and period, The frequency, f, and period, T, are reciprocals of each T, are reciprocals of each other.other.

• Tf 1

Speed of a WaveSpeed of a Wave

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

•Sound travels faster in solids Sound travels faster in solids than gases.than gases.

•Light travels faster in air than Light travels faster in air than water.water.

Calculating the Speed of a Calculating the Speed of a WaveWave

•v=fv=f•Where:Where:

•v is speed in m/sv is speed in m/s

•f is frequency in Hzf is frequency in Hz

• is wavelength in mis wavelength in m