Review:
What’s the difference between a transverse
and longitudinal wave?
What do waves transfer?
What are the high and low points of a
transverse wave called?
What are the parts of a longitudinal wave
where the particles are spread out and close
together?
First thing’s first…
• Which of these show ONE full wave?
One wave has one
crest and one
trough
Wavelength
• What is length a measure of?
• So what do you think a wave length is?
– The distance between two waves
WAVELENGTH
WAVELENGTH
Which has a shorter wavelength?
Measuring Wavelength
• Does this tell us the distance between
the two waves?
• Why not?
You have to measure the distance
between two comparable points!
(crest to crest, trough to trough, etc.)
Amplitude
• The distance between the crest or
trough and the wave’s resting position.
• Where’s the crest? Trough?
Trough
Amplitude
Amplitude
Crest
Resting
Position
Which has a larger amplitude?
What does amplitude tell us
about a wave?
• Which of these waves would cause more
damage if it hit the shore?
• Which has the larger amplitude?
• Which wave has more energy?
THAT’S
AMPLITUDE!
We’ve been looking at transverse
waves…What about longitudinal?
• We can relate all of the parts of a
transverse wave to a longitudinal one!
We’ll start with wavelength…
• In a transverse wave:
• But there aren’t any crests or troughs
in a longitudinal wave!
WAVELENGTH
WAVELENGTH
So we look at the compressions
and rarefactions!
• Compressions =
Crests
• Rarefactions =
Troughs
• Now we can find
the wavelength
– Compression to
compression
– Rarefaction to
rarefaction
On to amplitude…
• In a transverse wave:
• We now know that compressions are
rarefactions are like the crests and
troughs, but it’s hard to find a
longitudinal wave’s resting point.
Amplitude
• For the amplitude
of a longitudinal
wave, we look at
how compressed or
how rarefied the
spring or particles
are.
– The more
compressed or
rarefied it is, the
higher the
amplitude and vice
versa.
Frequency
• If your friend comes over to your house
“frequently”, how often do they come
over?
• Can you take a guess as to what the
“frequency” of a wave is?
– The frequency of a wave tells us the
number of waves that are produced in a
certain amount of time.
We need to know how many waves
are being produced in 10 seconds.
• How can you find the frequency of this
wave?
• Step 1: pick a point on the wave.
• Step 2: count the waves that pass that
point in 10 seconds.
Which has a higher frequency?
What is the unit for frequency?
• Frequency is measured in Hertz (Hz).
• If one full wave passes a point every
second, it has a frequency of 1 Hz.
– 1 wave per second (1 wave/1 sec.)
• What is the frequency if three waves
pass a point every second?
– 3 Hz. (3 waves/1 second)
• What is the frequency if six waves pass
a point every three seconds?
– 2 Hz. (6 waves/3 seconds)
Wave Speed
• There are two ways to calculate wave
speed.
– Option 1: time how long a wave takes to get
from point A to point B.
A
B
• Option 2: Use the following formula
Wave speed = wavelength x frequency
Wavelength – 2 meters
Frequency –
4 Hz.
(4 waves pass every second)
Wave Speed =
8 meters/second
• Wave speed is affected by several
factors
– The type of wave
• Example: electromagnetic waves always travel at
the same speed in a vacuum (300,000 km/s – the
speed of light)
– The medium the wave is moving through
• If you start two waves in a pan, one with water
and one with corn syrup, which will reach the
other side of the pan first?
• Another example is popping your knuckles
underwater as opposed to above water.