waves c1 nota tambahan

7/29/2019 Waves c1 Nota Tambahan

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UNIT EIGHT: Waves

Chapter 24 Waves and SoundChapter 25 Light and Optics


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Chapter Twenty-Four:Waves and Sound

24.1 Harmonic Motion

24.2 Properties of Waves

24.3 Sound


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Chapter 24.2 Learning Goals

Describe the properties and

behavior of waves.

Calculate the speed of waves.

Demonstrate an understanding of waveinteractions.


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Investigation 24B

Key Question:

How do waves move?

Waves in Motion


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24.2 What is a wave? A waveis an oscillation that travels from one

place to another.

If you poke a floating ball, it oscillates up anddown.

The oscillation spreads outward from where itstarted.


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24.2 WavesWhen you drop a ball into water, some

of the water is pushed aside and raised

by the ball.


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24.2 Parts of a wave

You can think of a wave as a moving series of

high points and low points. A crestis the high point of the wave.

A troughis the low point.


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The frequencyof a wave is the rate atwhich every point on the wave moves up

and down.

Frequency means how often.


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The amplitudeof a water wave is themaximum height the wave rises abovethe level surface.


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24.2 Parts of a wave Wavelengthis the distance from any point on

a wave to the same point on the next cycle ofthe wave.

The distance between one crest and the nextcrest is a wavelength.


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24.2 The speed ofwaves

A wave moves onewavelength in each cycle.

Since a cycle takes oneperiod, the speed of thewave is the wavelengthdivided by the period.


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24.2 The speed of waves The speed of a water wave is how fast the

wave spreads, NOT how fast the watersurface moves up and down or how fast the

dropped ball moves in the water.

How do we measure the wave speed?


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24.2 The speed of waves The speedis the distance traveled (one

wavelength) divided by the time it takes (one

period). We usually calculate the speed of a wave by

multiplying wavelength by frequency.


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Solving Problems

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

Calculate the frequency and the period ofthe wave.


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1. Looking for:

frequency in hertz

period in seconds

2. Given

= 1 m; s = 5 m/s

3. Relationships:

s = f x or f= s f= 1/Tor T = 1/f

4. Solution f= 5 m/s 1 m = 5 cycles/s

T = 1/5 cycles/s = .2 s

Solving Problems

f= 5 Hz

T = .2 s


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24.2 Four wave interactions When a wave encounters a

surface, four interactions

can occur:1. reflection,

2. refraction,

3. diffraction, or

4. absorption.


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24.2 Wave interactions

Diffraction usuallychanges the directionand shape of the wave.

When a plane wavepasses through a smallhole diffraction turns itinto a circular wave.


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24.2 Transverse and longitudinalwaves

A wave pulseis a short burst of a traveling

wave.

It is sometimes easier to see the motion ofwave pulses than it is to see long waves with

many oscillations.


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24.2 Transverse wavesThe oscillations of a transversewave are

notin the direction the wave moves.


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24.2 Longitudinal wavesThe oscillations of a longitudinalwave are

in the same direction that the wave

moves.


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24.2 Constructive interference Constructive interferencehappens when

waves add up to make a larger amplitude.

Suppose you make two wave pulses on astretched string.

One comes from the left and the other comesfrom the right.

When the waves meet, they combine to make asingle large pulse.


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24.2 Destructive interference

What happens when one pulse is on topof the string and the other is on the

bottom?

When the pulses meet in the middle, theycancel each other out.

During destructive interference, wavesadd up to make a wave with smaller orzero amplitude.


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waves c1 nota tambahan

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