WAVES
Simple Harmonic Motion
(SHM)
- sometimes called oscillatory motion
- the back and forth vibratory motion of
a swinging pendulum
- sine curve - the shape of the line a
swinging pendulum makes over a
constantly moving surface
What is a Wave?
A wave is a disturbance that carries
energy through matter or space.
Medium - the matter that a wave travels
through. Examples: water, air, steel,
the Earth
Types of Waves
Mechanical Waves - waves that require a
medium.
All waves, except light, are
mechanical waves.
Electromagnetic Waves - waves that
consist of changing electric and
magnetic fields in space.
Wave Characteristics
Crests - the high points of a wave
Troughs - the low points of a wave
Amplitude - the distance from the
midpoint to the crest (or trough) of a
wave
Wavelength - the distance between
successive identical parts of a wave
(crest to crest or trough to trough)
Parts of a Wave
Wave Characteristics
Period - the time it takes for one complete
wave
- time ÷ # of waves
- measured in time units
Frequency - the number of waves that pass a
point in a given amount of time
- # of waves ÷ time (usually seconds)
- measured in Hertz (Hz)
Frequency and Period
Period =
1
frequency
Frequency = 1
period
Problems
1. What is the frequency, in hertz, that
corresponds to each of the following
periods?
a. 0.10 s
b. 5 s
c. 1/60 s
d. 24 h
Problems
2. What is the period, in seconds, that
corresponds to each of the following
frequencies?
a. 10 Hz
b. 0.2 Hz
c. 60 Hz
d. 0.8 Hz
Problems
3. A metronome is set so that it makes
ten complete vibrations in 12 seconds.
Find the frequency of the metronome.
Wave Speed
In linear motion:
speed = distance (m/s)
time
In wave motion:
speed = wavelength x frequency
v=ƒ
(m · 1/s = m/s)
Problems
A wave with wavelength 10 m passes a
pier with a frequency of 2 Hz. What is
the speed of the wave?
Problems
A wave with wavelength 10 m passes a
pier with a frequency of 2 Hz. What is
the speed of the wave?
 = 10 m
 = 2 Hz
v=?
Problems
A wave with wavelength 10 m passes a
pier with a frequency of 2 Hz. What is
the speed of the wave?
 = 10 m
 = 2 Hz
v=?
v = 
v = (10m)(2Hz)
v = 20 m/s
Practice
If a water wave vibrates up and down
two times each second and the
distance between wave crests is 1.5 m,
what is the frequency of the wave?
What is its wavelength?
What is its speed?
Practice
If a water wave vibrates up and down
two times each second and the
distance between wave crests is 1.5 m,
what is the frequency of the wave?
 = 2 Hz
What is its wavelength?
 = 1.5 m
What is its speed?
v = 3 m/s
Practice
While sitting on a pier, Carlos notices
that incoming waves are 2.0 m
between crests. If the waves lap
against the pier every 0.5 s, find
a) the frequency.
b) the speed of the wave.
Practice
While sitting on a pier, Carlos notices
that incoming waves are 2.0 m
between crests. If the waves lap
against the pier every 0.5 s, find
a) the frequency.
 = 2 Hz
b) the speed of the wave.
v = 4 m/s
Kinds of Waves
Transverse Waves - the motion of the
medium is at right angles to the
direction in which the wave travels.
(Look like a sine curve.)
Example: water waves, light waves
Kinds of Waves
Longitudinal Waves - the particles move
along the direction of the wave (rather
than at right angles to it).
Example: sound waves
Standing Waves
Standing waves occur when the original
wave and the reflected wave combine
to form a wave where parts of the
medium do not move.
Standing Waves