Contributed by:
1. Describe the properties and behavior of waves.
2. Calculate the speed of waves.
3. Demonstrate an understanding of wave interactions.
2.
UNIT EIGHT: Waves
Chapter 24 Waves and
Sound
Chapter 25 Light and Optics
4.
Chapter Twenty-Four:
Waves and Sound
24.1 Harmonic Motion
24.2 Properties of Waves
24.3 Sound
5.
Chapter 24.2 Learning Goals
Describe the properties and
behavior of waves.
Calculate the speed of waves.
Demonstrate an understanding of
wave interactions.
6.
Investigation 24B
Waves in Motion
Key Question:
How do waves move?
7.
24.2 What is a wave?
A wave is an oscillation that travels
from one place to another.
If you poke a floating ball, it oscillates
up and down.
The oscillation spreads outward from
where it started.
8.
24.2 Waves
When you drop a ball into water,
some of the water is pushed
aside and raised by the ball.
9.
24.2 Parts of a wave
You can think of a wave as a moving
series of high points and low points.
A crest is the high point of the wave.
A trough is the low point.
10.
24.2 Parts of a wave
The frequency of a wave is the
rate at which every point on the
wave moves up and down.
Frequency means “how often”.
11.
24.2 Parts of a wave
The amplitude of a water wave is
the maximum height the wave
rises above the level surface.
12.
24.2 Parts of a wave
Wavelength is the distance from any
point on a wave to the same point on
the next cycle of the wave.
The distance between one crest and
the next crest is a wavelength.
14.
24.2 The speed
of waves
A wave moves one
wavelength in each
cycle.
Since a cycle takes
one period, the speed
of the wave is the
wavelength divided
by the period.
15.
24.2 The speed of waves
The speed of a water wave is how fast
the wave spreads, NOT how fast the
water surface moves up and down or
how fast the dropped ball moves in
the water.
How do we measure the wave speed?
16.
24.2 The speed of waves
The speed is 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.
18.
Solving Problems
The wavelength of a wave on a
string is 1 meter and its speed is 5
m/s.
Calculate the frequency and the
period of the wave.
19.
Solving Problems
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/T or T = 1/f
4. Solution
f = 5 m/s ÷1 m = 5 cycles/s f = 5 Hz
T = 1/5 cycles/s = .2 s T = .2 s
20.
24.2 Four wave interactions
When a wave encounters
a surface, four
interactions can occur:
1. reflection,
2. refraction,
3. diffraction, or
4. absorption.
22.
24.2 Wave interactions
Diffraction usually
changes the
direction and shape
of the wave.
When a plane wave
passes through a
small hole
diffraction turns it
into a circular wave.
23.
24.2 Transverse and
longitudinal waves
A wave pulse is a short ‘burst’ of a
traveling wave.
It is sometimes easier to see the
motion of wave pulses than it is to see
long waves with many oscillations.
24.
24.2 Transverse waves
The oscillations of a transverse wave are
not in the direction the wave moves.
26.
24.2 Longitudinal waves
The oscillations of a longitudinal
wave are in the same direction
that the wave moves.
28.
24.2 Constructive interference
Constructive interference happens
when waves add up to make a larger
amplitude.
Suppose you make two wave pulses on
a stretched string.
One comes from the left and the other
comes from the right.
When the waves meet, they combine to
make a single large pulse.
30.
24.2 Destructive interference
What happens when one pulse is
on top of the string and the other
is on the bottom?
When the pulses meet in the
middle, they cancel each other out.
During destructive interference,
waves add up to make a wave with
smaller or zero amplitude.
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