Characteristics of Characteristics of WavesWaves

What are waves?What are waves? WaveWave – – a disturbance that transfers energy from a disturbance that transfers energy from

place to place.place to place. MediumMedium – – the material through which a wave the material through which a wave

passespasses Waves travel through the medium without actually Waves travel through the medium without actually

moving the medium with it.moving the medium with it.

Types of Waves:Types of Waves: Transverse WavesTransverse Waves: waves that move the : waves that move the

medium at right angles to the direction in which medium at right angles to the direction in which the waves are traveling.the waves are traveling.

Longitudinal WavesLongitudinal Waves: move particles parallel to : move particles parallel to the direction the wave is moving, the direction the wave is moving, ““push-pullpush-pull” ” waves.waves.

Properties of WavesProperties of Waves AmplitudeAmplitude – – in a transverse wave in a transverse wave – – the height the height

away from the away from the ““restrest” ” position. The amplitude in a position. The amplitude in a longitudinal wave is the measure of how longitudinal wave is the measure of how compressed or rarefied the medium becomes.compressed or rarefied the medium becomes.

WavelengthWavelength – – the distance between two the distance between two corresponding parts of a wave.corresponding parts of a wave.

FrequencyFrequency – – the number of complete waves that the number of complete waves that pass a given point in a certain period of time. pass a given point in a certain period of time. Frequency is measured in Frequency is measured in HERTZHERTZ, one , one HzHz is a is a wave that occurs once every second.wave that occurs once every second.

SpeedSpeed (meters/sec)= wavelength x frequency (meters/sec)= wavelength x frequency FrequencyFrequency (Hz = 1/sec)= speed / Wavelength (Hz = 1/sec)= speed / Wavelength WavelengthWavelength (meters) = speed / Frequency (meters) = speed / Frequency

Designated by Greek letter lambda - Designated by Greek letter lambda -

Speed Frequency & Speed Frequency & WavelengthWavelength

Speed

Wavelength x frequency

S

x f

S = x f = 1.5 m x 280 Hz = 420 m/s

= S / f = 5.0 m/s / 2.5 Hz = 2 m

Interactions of WavesInteractions of Waves Absorption- Absorption- wave taken in.wave taken in. RefractionRefraction – – The bending of a wave due to the wave The bending of a wave due to the wave

moving from one type of medium into another.moving from one type of medium into another. ReflectionReflection – – Bounce back waveBounce back wave

Angle of Incidence Angle of Incidence is the angle of the wave coming into the is the angle of the wave coming into the object reflecting the wave.object reflecting the wave.

Angle of Reflection Angle of Reflection is the angle bouncing off and going away is the angle bouncing off and going away from the object.from the object.

DiffractionDiffraction – – Wave passing a barrier or Wave passing a barrier or going through a hole in a barrier bends going through a hole in a barrier bends and causes the wave to wrap around the and causes the wave to wrap around the barrierbarrier

Interactions of WavesInteractions of Waves

InterferenceInterference – when two or more waves meet, they – when two or more waves meet, they interact. This interaction is called interference.interact. This interaction is called interference. 1. 1. Constructive Interference Constructive Interference – the combining of waves – the combining of waves

to cause higher amplitude of any of the original waves.to cause higher amplitude of any of the original waves. 2. 2. Destructive Interference Destructive Interference – when the combining of the – when the combining of the

waves produce a new wave with a smaller amplitude than waves produce a new wave with a smaller amplitude than the beginning wavesthe beginning waves

Interactions of WavesInteractions of Waves

Standing WavesStanding Waves Standing Waves Standing Waves – – the combining of the incoming and the combining of the incoming and

reflected wave so that the resultant appears to be standing stillreflected wave so that the resultant appears to be standing still NodeNode – – the point where Constructive Interference and the point where Constructive Interference and

Destructive Interference cause an amplitude of zero on the Destructive Interference cause an amplitude of zero on the standing wave.standing wave.

AntinodeAntinode – – the point where Constructive Interference and the point where Constructive Interference and Destructive Interference of a standing wave are represented by Destructive Interference of a standing wave are represented by the crest and the trough.the crest and the trough.

ResonanceResonance – – the point where vibrations traveling thru and the point where vibrations traveling thru and object matches the natural vibrations of an object. I.e. an opera object matches the natural vibrations of an object. I.e. an opera singer hitting a note and shattering a crystal glass.singer hitting a note and shattering a crystal glass.

Natural Frequency- Natural Frequency- Frequency where you create one standing Frequency where you create one standing wave.wave.

HarmonicsHarmonics- Multiples of Natural Frequency- Multiples of Natural Frequency

Wiggler LabWiggler Lab Using the wiggler device, discover the Using the wiggler device, discover the

natural frequency of your string (when you natural frequency of your string (when you make 1 standing wave. Record wavelength make 1 standing wave. Record wavelength (cm), amplitude (cm), frequency (Hz) and (cm), amplitude (cm), frequency (Hz) and calculate speed of the wave (cm/s).calculate speed of the wave (cm/s).

Find as many harmonics (multiple of natural Find as many harmonics (multiple of natural frequencies) as you can. Record the same frequencies) as you can. Record the same data and do the same calculations as above.data and do the same calculations as above.

Now tighten or loosen the string and find Now tighten or loosen the string and find your new natural frequency. Conclude how your new natural frequency. Conclude how tension of the string affects the natural tension of the string affects the natural frequency.frequency.

Seismic WavesSeismic Waves Seismic Waves Seismic Waves – – waves caused by waves caused by

the release of energy due to the release of energy due to earthquakes composed of earthquakes composed of P - primary wavesP - primary waves S - secondary wavesS - secondary waves L - surface wavesL - surface waves

P WavesP Waves P waves P waves –- –- Primary waves are pPrimary waves are pressure ressure

waves & waves & are the fastest moving waves, are the fastest moving waves, they travel thru solids and liquids, Push-they travel thru solids and liquids, Push-Pull Waves AKA Longitudinal wavesPull Waves AKA Longitudinal waves

S WavesS Waves S Waves S Waves – – Secondary Waves are slower Secondary Waves are slower

than primary waves, they cannot travel than primary waves, they cannot travel thru liquid and are Transverse Waves.thru liquid and are Transverse Waves.

L WavesL Waves L Waves (last waves) Surface wave L Waves (last waves) Surface wave – – the the

combination on the Earthcombination on the Earth’’s surface of Primary s surface of Primary and Secondary waves. and Secondary waves. The rolling chaotic movement of the surfaceThe rolling chaotic movement of the surface Cause the most damage of the seismic wavesCause the most damage of the seismic waves

All Done… No mas…All Done… No mas…No more on “waves”No more on “waves”

Keep an eye out for the Keep an eye out for the next next

slide show on slide show on “Sound”“Sound”

Chapter 8Chapter 8TTFNTTFN