What are
waves?
Wave
Definition: A disturbance that transfers
energy from place to place.
What carries waves? A medium, a
medium is the material through which a
wave travels.
A medium can be a gas, liquid, or solid.
Not all waves require a
medium to travel.
Mechanical Waves are waves that
require a medium.
Electromagnetic Waves travel through
empty space and do not require a
medium.
What causes waves?
Waves are created
when a source of
energy causes a
medium to vibrate.
A vibration is a
repeated back and
forth or up and
down motion.
How do waves carry energy?
Waves carry energy by displacement
The energy from this initial displacement
causes the material nearby to also displace,
which in turn displaces material near it...
which creates a wave of energy propagating
outwards.
It is important to note that the material may
move around as the wave passes, but it is the
energy which is propagating outwards, not
the material itself.
Lab: Slinkys in Action
Use a slinky to
make different
types of waves.
Notice how the
ribbon moves
with each
different type of
wave.
Where did the
energy come
from to start the
wave?
How could you
tell the wave
carried energy?
Types of waves: Waves are
classified according to how
they move.
Transverse Wave
Teacher’s Domain Animation
Use a marker to trace a particles motion as
the wave travels through the medium.
How does the particle move with respect to
the direction of the wave?
Transverse wave
Waves that move the
medium at right angles
to the direction in which
the waves are traveling
is called a transverse
wave 3:15min.
Transverse means
across. The highest
parts are called crests
the lowest parts are
called troughs.
(sometimes called a sine curve or wave)
Draw & Label a
Transverse Wave
Compressional or Longitudinal
Wave
Matter vibrates in the
same direction as the
wave travels.
Longitudinal discussion 3:36 min
Compressional or Longitudinal
wave
The parts, where
the coils are close
together are called
compressions, the
parts where the coils
are spread out are
called rarefactions.
Teacher’s Domain
animation
Draw & Label a
Compressional/Longitudinal
Wave
Longitudinal & Transverse Wave
Animation
Longitudinal & Transverse Wave
Animation #2
Combinations of waves
Surface waves are a
combination of
transverse and
longitudinal waves. The
waves occur at the
surface between water
and air.
Surface Wave
Animation
Summary of Waves
Summary of Waves - NASA
Launch Pad Video Clip
Review, Review, Review…
What does a wave carry?
How can waves be generated?
Compare and contrast a longitudinal
and transverse wave.
Properties of Waves
Basic Properties of Waves
Amplitude
Wavelength
Frequency
Speed
Amplitude
Amplitude is the maximum (displacement) distance the
particles of the medium carrying the wave move away
from their rest positions.
The farther the medium moves as it vibrates the larger the
amplitude of the resulting waves. The greater the
amplitude the greater the amount of energy.
Amplitude of transverse waves
The amplitude of a transverse wave is
the maximum distance the medium
moves up or down from its rest
position.
You can find the amplitude of a
transverse wave by measuring the
distance from rest to crest or rest to
trough.
Amplitude of a longitudinal
wave.
The amplitude of a longitudinal wave is
a measure of how compressed or
rarefied the medium becomes.
Same frequencies, same wavelengths,
different amplitudes, different energy
Wavelength
A wave travels a certain distance before
it starts to repeat. The distance
between two corresponding parts
of a wave is its wavelength.
Transverse measure from crest to crest
or trough to trough.
Longitudinal measure from one
compression to the next.
Frequency
The number of complete waves that
pass a given point in a certain amount
of time.
AKA number of vibrations per second.
Frequency measured in hertz (Hz)
named after Heinrich Hertz who
discovered radio waves in 1886.
Frequency Animation
Period
The period of a wave is the time for a
particle to make one complete cycle.
Pair Share
1. Is there a relationship between
wavelength and frequency? What is it?
2. Is there a relationship between
frequency and period? What is it?
3. Is there a relationship between
amplitude and frequency? What is it?
1. Yes. A decrease in the wavelength
increases the frequency and vice versa.
2. Yes. An increase in the frequency will
increase the period and vice versa.
3. NO! Putting a lot of energy into a wave will not affect
the wavelength, the frequency or the speed of the
wave. The energy imparted to a wave will only affect
the amplitude of that wave.
Speed
The speed, wavelength, and frequency
of a wave are related to each other by a
mathematical formula.
Speed = wavelength x frequency
Frequency = speed/wavelength
Wavelength = speed/frequency
Speed
What can effect the speed of a wave?
Wave speed depends upon the
medium through which the wave is
moving. Only an alteration in the
properties of the medium will
cause a change in the speed.
Speed
Waves in different
mediums travel at
different speeds.
However, in a given
medium and under
the same conditions
the speed of the
wave is constant.
1. A teacher attaches a slinky to the wall and begins
introducing pulses with different amplitudes. Which of the
two pulses (A or B) below will travel from the hand to the
wall in the least amount of time? Justify your answer.
They reach the wall at the same time. Don't be
fooled! The amplitude of a wave does not affect the
speed at which the wave travels. Both Wave A and
Wave B travel at the same speed. The speed of a
wave is only altered by alterations in the properties
of the medium through which it travels.
2. The teacher then begins introducing pulses with a
different wavelength. Which of the two pulses (C or D)
will travel from the hand to the wall in the least amount
of time ? Justify your answer.
They reach the wall at the same time. Don't be
fooled! The wavelength of a wave does not affect the
speed at which the wave travels. Both Wave C and
Wave D travel at the same speed. The speed of a
wave is only altered by alterations in the properties
of the medium through which it travels.
3. Two waves are traveling through the same
container of nitrogen gas. Wave A has a wavelength
of 1.5 m. Wave B has a wavelength of 4.5 m. The
speed of wave B must be ________ the speed of
wave A.
a. one-ninth
b. one-third
c. the same as
d. three times larger than
Answer: C
The medium is the same for both of these waves
("the same container of nitrogen gas"). Thus, the
speed of the wave will be the same. Alterations in a
property of a wave (such as wavelength) will not
affect the speed of the wave. Two different waves
travel with the same speed when present in the same
medium.
4. TRUE or FALSE:
Doubling the frequency of a wave
source doubles the speed of the waves.
FALSE!
The speed of a wave is unaffected by
changes in the frequency.
5. A wave is introduced into a thin wire
held tight at each end. It has an
amplitude of 3.8 cm, a frequency of
51.2 Hz and a distance from a crest to
the neighboring trough of 12.8 cm.
Determine the period of such a wave.
Answer: 0.0195 sec
Here is an example of a problem with a lot of
extraneous information. The period is simply the
reciprocal of the frequency. In this case, the period is
Period T =___1___
51.2 Hz
T = 0.0195 seconds.
6. Frieda the fly flaps its wings back
and forth 121 times each second. The
period of the wing flapping is ____ sec.
Answer: 0.00826 seconds
The quantity 121 cycles/second
(times/second) is the frequency
T (period)=___1__sec__
cycles
121 sec ond
T(period)= 0.00826 s
7. A tennis coach paces back and forth
along the sideline 10 times in 2
minutes. The frequency of her pacing is
________ Hz.
a. 5.0
b. 0.20
c. 0.12
d. 0.083
Answer: D
Frequency refers to the number of occurrences of a
periodic event per time and is measured in
cycles/second. In this case, there are 10 cycles per 2
minutes (also known as 10 cycles per 120 seconds).
So the frequency is
f =10 cycles
120 s
f= 0.0833 cycles/s
Cicadas produce a buzzing sound that
has a wavelength in air of 2.69 m. If
the speed of sound in air is 346 m/s,
what is the frequency of the sound
produced by a cicada? What is its
period?
One of the largest organ pipes is in the
auditorium organ in the convention hall
in Atlantic City, New Jersey. The pipe is
38.6 ft long and produces a sound with
a wavelength of about 10.6 m. If the
speed of sound in air is 346m/s, what is
the frequency of this sound?
A wave with a frequency of 60 Hz
(cycles/second) travels through
vulcanized rubber with a wavelength of
.90 m. What is the speed of wave?
A wave with a frequency of 60 Hz
(cycles/second) travels through steel
with a wavelength of 85.5 m. What is
the speed of this wave?
A dolphin can typically hear sounds with
frequencies up to 150 kHz. What is the
speed of sound in water if a wave with
this frequency has a wavelength of 1.0
cm?
A ship anchored at sea is rocked by
waves that have crests 14 m apart.
The waves travel 7 m/s. How often do
the waves crests reach the ship?
Earthquakes generate shock waves that
travel through Earth’s interior to other
parts of the world. The fastest of these
waves are longitudinal waves, like
sound waves, and are called primary
waves, or just p-waves. A p-wave has
a very low frequency, typically around
.0050 Hz. If the speed of a p-wave
with this frequency is 8.0 km/s, what is
its wavelength?
8. Mac and Tosh are resting on top of
the water near the end of the pool
when Mac creates a surface wave. The
wave travels the length of the pool and
back in 25 seconds. The pool is 25
meters long. Determine the speed of
the wave
GIVEN: d (1-way) =25 m, t (2-way)=25 s
Find v.
If the pool is 25 meters long, then the back-and-forth
distance is 50 meters. The wave covers this distance
in 25 seconds. Now use v = d / t.
v = d / t = (50 m) / (25 s) = 2 m/s
9. The water waves below are traveling along the
surface of the ocean at a speed of 2.5 m/s and
splashing periodically against Wilbert's perch. Each
adjacent crest is 5 meters apart. The crests splash
Wilbert's feet upon reaching his perch. How much time
passes between each successive drenching? Answer
and explain using complete sentences.
If the wave travels 2.5 meters in one
second then it will travel 5.0 meters in
2.0 seconds. If Wilbert gets drenched
every time the wave has traveled 5.0
meters, then he will get drenched every
2.0 seconds.
10.While hiking through a canyon, Noah
Formula lets out a scream. An echo is
heard 0.82 seconds after the scream.
The speed of the sound wave in air is
342 m/s. Calculate the distance from
Noah to the nearby canyon wall.
GIVEN: v = 342 m/s, t = 0.82 s (2-way)
Find d (1-way)
If it takes 0.82 s to travel to the canyon wall and
back (a down-and-back time), then it takes 0.41 s to
travel the one-way distance to the wall. Now use d =
v•t
d = v • t = (342 m/s) • (0.41 s) = 140 m
Chapter 15 -3
Ways Waves Interact
Reflection
Refraction
Diffraction
Interference
Constructive
Destructive
Standing Waves
Reflection
When an object or
wave hits a surface
through which it
cannot pass, it
bounces back.
Angle of incidence
Angle of reflection
Examples of reflection
Mirror
Echo
Ball against a wall
Refraction is when a wave
moves from one medium into
another medium at an angle,
it changes speed as it enters
the second medium which
causes it to bend. The
bending of waves due to a
change in speed is called
refraction.
Refraction
Though all waves
change speed when
they enter a new
medium. Bending
occurs when one
side of the wave
enters the new
medium before the
other side
Diffraction
When a wave passes a barrier or moves
through a hole in a barrier it bends and
spreads out.
Interference
Constructive interference occurs
whenever two waves combine to make
a wave with a larger amplitude.
Destructive interference when the
amplitudes of two waves combine
producing a smaller amplitude.
Standing waves:
If the incoming wave and the reflected
wave combine at the right places the
combined wave appears to be standing
still.
It appears to be standing in one place,
even though it is two waves interfering
as they pass through each other.
Brightstorm video 9:45 min
Nodes and Antinodes
Nodes: at certain
points, destructive
interference causes
the two waves to
combine and
produce an
amplitude of zero.
Antinodes are the
points of maximum
energy. The crests
and troughs of a
standing wave.
Resonance
Most objects have a natural frequency of
vibration. Resonance occurs when vibrations
traveling through an object match the object’s
natural frequency.
An object that is vibrating at its natural frequency
absorbs energy from the objects that vibrate at
the same frequency. Occurs in music.