WavesWaves

23.2 – Properties of Waves23.2 – Properties of Waves

pp. 562 - 566pp. 562 - 566

23.2 Waves23.2 Waves• A A wavewave is an oscillation that travels from is an oscillation that travels from

one place to another.one place to another.• If you poke a floating ball, it oscillates up If you poke a floating ball, it oscillates up

and down.and down.• The oscillation spreads outward from The oscillation spreads outward from

where it started.where it started.

23.2 Waves23.2 Waves• When you drop a ball into water, When you drop a ball into water,

some of the water is pushed aside some of the water is pushed aside and raised by the ball.and raised by the ball.

23.2 Waves23.2 Waves

• Waves are a Waves are a traveling form of traveling form of energy because they energy because they can change motioncan change motion..

• Waves also carry Waves also carry informationinformation, such as , such as sound, pictures, or sound, pictures, or even numbers.even numbers.

23.2 Frequency, amplitude, 23.2 Frequency, amplitude, and wavelengthand wavelength• You can think of a wave as a moving You can think of a wave as a moving

series of high points and low points.series of high points and low points.• A A crestcrest is the high point of the wave.is the high point of the wave.• A A ttroughrough is the low point.is the low point.

TERMS TO LEARNTERMS TO LEARN

• Amplitude – Amplitude – the maximum distance a the maximum distance a wave vibrates from its resting wave vibrates from its resting positionposition

• Resting position – Resting position – where the particles where the particles of a medium stay when there are no of a medium stay when there are no disturbancesdisturbances

TERMS TO LEARNTERMS TO LEARN

•Wavelength – Wavelength – the distance the distance between one point on one wave to between one point on one wave to the same point on the next wavethe same point on the next wave

•Frequency – Frequency – the number of waves the number of waves produced in a certain amount of produced in a certain amount of timetime

•Wave speed – Wave speed – the speed at which the speed at which a wave travelsa wave travels

PROPERTIES OF WAVESPROPERTIES OF WAVES

•AmplitudeAmplitude

•WavelengthWavelength

•FrequencyFrequency

•Wave speedWave speed

AMPLITUDEAMPLITUDE

•Distance where the greatest Distance where the greatest movement from rest occurs.movement from rest occurs.

•The larger the amplitude is, the The larger the amplitude is, the taller the wave is and taller the wave is and the more the more energy it hasenergy it has

•The smaller the amplitude, the The smaller the amplitude, the shorter the wave is and shorter the wave is and the less the less energy it has.energy it has.

AMPLITUDEAMPLITUDE

•Amplitude of a Amplitude of a transverse transverse wave is wave is measured from measured from the the resting resting position to the position to the crest or resting crest or resting position to position to trough.trough.

WAVELENGTHWAVELENGTH

• On a transverse On a transverse wave, wavelength is wave, wavelength is the distance the distance between between two two adjacent crests, adjacent crests, troughs or any one troughs or any one point on one wave point on one wave to the corresponding to the corresponding point on the next point on the next wavewave..

WAVELENGTHWAVELENGTH

• On a longitudinal wave, wavelength is the On a longitudinal wave, wavelength is the distance between two adjacent distance between two adjacent compressionscompressions, , rarefactions or any one point on one wave to rarefactions or any one point on one wave to the corresponding point on the next wave.the corresponding point on the next wave.

WAVELENGTHWAVELENGTH

•Wavelength is measured in Wavelength is measured in metersmeters

•The symbol for The symbol for wavelengthwavelength is is λλ

FREQUENCYFREQUENCY

• Frequency is the Frequency is the number of complete number of complete waves (or cycles) produced in a waves (or cycles) produced in a specific unit of time.specific unit of time.

• Frequency is measured in Frequency is measured in HertzHertz (Hz). (Hz).

• 1 Hz = 1 cycle/second1 Hz = 1 cycle/second

• 1 Hz = 1/s1 Hz = 1/s

FREQUENCYFREQUENCY

• For a transverse wave, For a transverse wave, count the count the number of crests or troughs that number of crests or troughs that pass a point in a given amount of pass a point in a given amount of time.time.

• For a longitudinal wave, For a longitudinal wave, count the count the number of compressions or number of compressions or rarefactions that pass a point in a rarefactions that pass a point in a given amount of timegiven amount of time..

FREQUENCYFREQUENCY

• The frequency of a wave is related to its The frequency of a wave is related to its wavelengthwavelength..

• At a given speed, the At a given speed, the higher the frequencyhigher the frequency of the wave, of the wave, the shorter the wavelength isthe shorter the wavelength is..

23.2 The speed of waves23.2 The speed of waves• The speed of a water wave is how The speed of a water wave is how fast fast

the wave spreadsthe wave spreads, NOT how fast the , NOT how fast the water surface moves up and down or how water surface moves up and down or how fast the dropped ball moves in the water.fast the dropped ball moves in the water.

How do we measure the wave speed?

WAVE SPEEDWAVE SPEED

• Found by measuring the distance a Found by measuring the distance a single crest (or compression) travels single crest (or compression) travels in a given amount of time.in a given amount of time.

• Wave speed depends on the Wave speed depends on the medium medium through which the wave is traveling.through which the wave is traveling. (Ex.: speed of sound in air = 340 (Ex.: speed of sound in air = 340 m/s; speed of sound in steel = 5200 m/s; speed of sound in steel = 5200 m/s)m/s)

WAVE SPEEDWAVE SPEED

•Formula for calculating wave speed:Formula for calculating wave speed:

• V= f V= f λλ – where v = speed (measured in m/s)where v = speed (measured in m/s)– f = frequency (measured in Hz)f = frequency (measured in Hz)– λλ = wavelength (measured in m) = wavelength (measured in m)

Solving ProblemsSolving Problems

• The wavelength of a wave on a string The wavelength of a wave on a string is 1 meter and its speed is 5 m/s.is 1 meter and its speed is 5 m/s.

• Calculate the frequency and the Calculate the frequency and the period of the wave.period of the wave.

1.1. Looking for: Looking for: – ……frequency in hertzfrequency in hertz– ……period in secondsperiod in seconds

2.2. GivenGiven– …… = 1 m; s = 5 m/s= 1 m; s = 5 m/s

3.3. Relationships:Relationships:– v = v = f x f x or or f f = v = v ÷ ÷ – f f = 1/T= 1/T or T = 1/or T = 1/f f

4.4. SolutionSolution– f f = 5 m/s = 5 m/s ÷÷1 m = 5 1 m = 5

cycles/scycles/s– T = 1/5 cycles/s = .2 sT = 1/5 cycles/s = .2 s

Solving ProblemsSolving Problems

f = 5 Hz

T = .2 s

Solving ProblemsSolving Problems

• Complete Your Turn on p. 565 of Complete Your Turn on p. 565 of text.text.