23.2 Waves
A wave is an oscillation that travels from
one place to another.
If you poke a floating ball, it oscillates up
and down.
23.2 Waves
When you drop a ball into water,
some of the water is pushed aside
and raised by the ball.
The oscillation spreads outward from
where it started.
23.2 Waves
Waves are a
traveling form of
energy because they
can change motion.
23.2 Frequency, amplitude, and
wavelength
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.
Waves also carry
information, such as
sound, pictures, or
even numbers.
23.2 Frequency
23.2 Wavelength
The frequency of a wave is the rate
at which every point on the wave
moves up and down.
Wavelength is the distance from any point
on a wave to the same point on the next
cycle of the wave.
Frequency means “how often”.
The distance between one crest and the
next crest is a wavelength.
Measured in hertz (Hz)
A crest is the high point of the wave.
Carried to every place the wave goes
A trough is the low point.
1
Motion
23.2 Amplitude
The amplitude of a water wave is the
maximum height the wave rises
above the level surface.
Also determined by one-half the distance
between the crest and trough of a wave
23.2 The speed of waves
The speed of a water wave is how fast
the wave spreads from where it begins,
NOT how fast the water surface moves up
and down or how fast the dropped ball
moves in the water.
The wave front is the leading edge of
a moving wave.
A plane wave – moving waves with crests
in parallel straight lines
A circular wave has crests forming a circle
around a point where the wave began
23.2 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.
How do we measure the wave speed?
23.2 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.
Copy equation into
bottom box on the
right
2
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.
3. Relationships:
1. Looking for:
v = f x λ or f = v / λ
…frequency in hertz
f = 1/T or T = 1/f
…period in seconds
4. Solution
2. Given
f = 5 m/s ÷1 m = 5 cycles/s
…λ = 1 m; v = 5 m/s
T = 1/5 cycles/s = 0.2 s
f = 5 Hz
T = 0.2 s
3