2. What Are Waves?
Wave – a disturbance that transfers energy
-- the energy transferred through a wave can be
carried from the disturbance, through the wave, to another
object
Ex: wind gives energy (a disturbance), creating waves
on an ocean, and the ocean carries that energy to a boat, and
the energy rocks the boat up and down
-- the energy from the disturbance is transferred
through a medium
3. Mediums
Medium – the substance through which a wave travels
-- in an ocean wave, water is the medium
-- in sound waves, air is the medium
It is important to understand that the wave DOES NOT
CARRY the medium itself. It only moves energy through
the medium.
-- the ship doesn’t move on the waves, it only bobs
up and down
4. What Causes Waves?
Waves are created when a source of energy causes a
vibration in a medium
Vibration – a repeated back-and-forth or up-and-down
motion
-- some mediums can vibrate a lot with only a little
energy input
-- other mediums only vibrate a little with a lot of
energy input
-- the amount of vibration depends on the
spacing and type of molecules within the
medium
5. Types of Waves
There are three different types of waves, which are solely
characterized by the way that they move.
The three types of waves are:
-- Transverse waves
-- Longitudinal Waves
-- Surface Waves
6. Transverse Waves
Transverse waves – waves whose mediums move a right
angles (perpindicular) to the direction of overall wave travel
-- if the wave below moves left-to-right, the medium
will move up-and-down
-- like whipping a rope
Parts of a Transverse Wave
Crest – the “high” parts of the transverse wave
Trough – the “low” parts of the transverse wave
7. Longitudinal Waves
Longitudinal Waves – waves whose mediums move in the
same direction as overall wave travel
-- like squeezing and releasing a slinky spring
-- longitudinal waves are often called compressional
waves
Parts of a Longitudinal wave
Compressions – areas where the molecules in the
medium are tightly squeezed together
Rarefactions – areas where the molecules in the
medium are spread apart
8. Surface Waves
Surface Waves – waves that form at the boundary between
two different mediums
-- the bouncing of waves vibrating differently create
circular-shaped waves
9. Wave Properties
Despite the different types of waves, all waves share the
same basic properties:
-- amplitude
-- wavelength
-- frequency
-- speed
When figuring out these properties on either longitudinal or
transverse waves, it is necessary to remember the following:
Crests on a transverse wave are equal to compressions on
a longitudinal wave
Troughs on a transverse wave are equal to rarefactions on
a longitudinal wave
10. Amplitude
Amplitude – the maximum distance the particles of a
medium move from their rest position
For a transverse wave:
-- to find amplitude, you measure the height of the
crest from the REST POSITION (or the depth of the trough)
For a longitudinal wave:
-- to find amplitude, you measure how strongly
compressed the compressions are (or how far apart the
rarefactions are spread)
amplitude
11. Wavelength
Wavelength – how much of the medium is between
corresponding parts of a repeating wave
-- wavelength is measured in meters, and is
represented in formulas by the Greek letter lambda (λ)
For a transverse wave:
-- you find wavelength by measuring the distance
between crests (or troughs)
For a longitudinal wave:
-- you find wavelength by measuring the distance
between compressions (or rarefactions)
wavelength
12. Frequency
Frequency – the number of complete waves that pass a
specific point in a given amount of time (usually 1 second)
-- frequency is measured in a unit called Hertz (Hz),
which is equal to waves/second (really is the unit per second)
-- frequency is represented by the Greek letter nu (ν)
To find the frequency of any wave, either count the number of
crests or the number of compressions that pass a specific
point in a given amount of time, then solve
Period – the amount of time it takes for one complete wave to
pass
-- period is the inverse of frequency
Ex: If a wave has a frequency of 3 Hz (3 waves pass per
second, then its period is 1/3 second (it takes 1/3 of a second
13. Speed
The speed of a wave is how much of a medium passes by a
specific point in a given amount of time
-- speed is in the units of meters per second (m/s)
The speed of the wave is entirely determined by the medium
through which the wave passes.
We can calculated wave speed with the following equation:
Speed = wavelength x frequency
OR
s = λ x ν
Of course: λ = (s / ν) and ν = (s / λ)
vs /
14. Practice Problems
1. An ocean wave passes a buoy 5 times in 20 seconds.
a) What is the frequency of this wave?
b) What is the period of this wave?
c) If the wave has a wavelength of 10 meters, what is the
speed of this wave?
15. More Practice Problems
2. The speed of a rope is 40 m/s and its wavelength is 5 m.
a) What is the frequency of this wave?
b) What is the period of this wave?
3. A wave with a period of 0.2 seconds travels at a speed of
60 m/s. What is the wavelength of this wave?
