1. WAVES AND VIBRATIONS NOTES

2. A wave is a vibration moving in time and space
It cannot exist in one place but must
extend from one place to another
Wave motion is a way to transfer energy without
transfer of matter

3. A vibration is back and forth movement
A single disturbance or vibration is a wave pulse
If the source repeatedly vibrates it produces periodic motion

4. Demonstration: What happens when a tuning fork is placed in water?
Sound is produced when matter vibrates
Demonstration: What happens when a tuning fork
is placed in water?
Since sound is produced when matter vibrates,
sound is a form of mechanical energy.

5. Crest
midpoint
trough
Crest: High point in the wave
Trough: Low point in the wave
Midpoint of wave where the wave is in equilibrium
Amplitude Distance from the midpoint to the crest or trough
The higher the amplitude the stronger the wave

6. Wavelength is: the distance from one point on the wave to
the identical point on the next wave.
Crest to Crest, or trough to trough

7. How many wavelengths or wave cycles pass in one second.
 Frequency is: How frequently a vibration occurs.
How many wavelengths or wave cycles pass in one second.
If 2 wavelengths (or vibrations, or wave cycles) pass a
point in one second, then the frequency is:
2 vibrations/ second. (Or 2 cycles/ sec)

8. Hertz is: a unit of frequency (abbreviated Hz) It was named after
It was named after
Heinrich Hertz
who demonstrated
radio waves in 1886.
One vibration per second is one Hertz.
2 vibrations (or waves, or cycles) per
second is ________Hertz 2

9. Longer vibrations, so lower sound
DEMONSTRATIONS:
Hacksaw blade: (hold blade against table edge.
Change length hanging over and vibrate it.
Describe the frequency of vibration and pitch
(highness or lowness of the sound) when the hacksaw blade is long.
Longer vibrations, so lower sound
Describe the frequency of vibration and pitch when the
hacksaw blade is shorter.
Higher vibrations so higher pitch

10. What is the relationship between the amount of water
Containers with water. (pop bottles
to blow across or crystal glass to rub
finger around) 
What is the relationship between the amount of water
in each container and the pitch?
Less water vibrating means higher pitch.
More water vibrating is lower pitch
The longer the length of vibrating air above the water,
the Lower the pitch when blowing into a bottle

11. If a wave's frequency is known, then you can calculate
the period of time it takes for one wave to pass.
If the frequency is 2 Hz, then the time it takes for
1 vibration is ½ second .
Explain the relationship between Period and Frequency:
Frequency = Period =
Period (T) Frequency
It is an inverse relationship
If freq = 5 Hz then Period = 1/5 or .2 seconds

12. The Sears Building in
Chicago sways back and forth
at a vibration frequency of 0.1 Hz.
What is its Period of vibration?
T = 1 / f
1 / 0.1 cycles/sec = 10 seconds/cycle
It takes 10 seconds for it to sway back
and forth one time

13. Speed of a wave depends on the medium through which the wave travels.
WAVE SPEED
Speed of a wave depends on the medium
through which the wave travels.
Speed depends on:
Density of materials how many molecules there
are to bump into each other
Elasticity how well it changes shape and then
springs back. More elastic, the faster the
waves travel.
Temperature higher the temperature,
the faster the molecules move
Sound travels about 330 m/s m/s depending on the temperature of the air. It travels 4 times faster in water, and 15 times faster in steel.

14. λ Greek letter Lambda = wavelength
Wave Speed = frequency x wavelength
λ Greek letter Lambda = wavelength
Wave Speed
Freq. λ

15. Sound waves at a concert reach your ears at the
Frequency (Hz) Wavelength (m) Wave Speed (m/s)
Sound waves at a concert reach your ears at the
same time. Lower notes have long waves,
high notes (higher frequency) have shorter wave lengths,
but they all have the same wave speed.

16. If a water wave vibrates up and down 2 times each
second and the distance between wave crests is 1.5 meters,
what is the frequency of the wave?
What is its wavelength? What is its speed?
F = 2 Hz Wavelength = 1.5 m
Speed = 2 cycles x m = 3 m/sec
Sec Cycle

17. What is the wavelength of a 340 Hz sound wave when
the speed of sound in air is 340 m/s?
Wavelength = speed = 340 m/sec = 1 meter/cycle
Frequency cycles/sec
1 miles = 1609 meters. If the speed of sound is 340 m/s,
how long does it take for thunder to travel 1 mile?
T = distance/speed m = 4.7 seconds
340 m/sec
So about 5 seconds/mile

18. TRANSVERSE WAVES
Motion of the wave is at right angles to the direction of travel
Examples: waves on the surface of liquids,
Radio waves, light waves
slinky demo

19. LONGITUDINAL WAVES
motion of waves is in the same direction

20. Examples: sound waves
SMOKE RINGS

21. AS A REVIEW OF THE WAVE TYPES
Transverse
rarefaction
Longitudinal
compression

22. NATURAL FREQUENCY:
When you drop a wrench and baseball bat on the
floor, you hear 2 different sounds. They vibrate
differently. When any object composed of an elastic
material is disturbed it vibrates at its own special set
of frequencies. This natural frequency depends on
factors such as:
elasticity and the shape of the object
RESONANCE:
When the vibration of one object causes another object to:
vibrate at its natural frequency
A dramatic increase in Amplitude occurs.

23. Swinging on a swing pump in rhythm with natural frequency of the
Examples of Resonance
Swinging on a swing pump in
rhythm with natural frequency of the
swing, go higher and higher
Tuning fork can cause another to vibrate
Tacoma Narrows Bridge
destroyed by a 40 mph wind
(video)
Wine glass shattering

24. Constructive Interference: when one wave crest
INTERFERENCE OF WAVES
Constructive Interference: when one wave crest
overlaps another crest and they build together
Animation courtesy of Dr. Dan Russell, Kettering University

25. Destructive Interference: when one wave crest
Destructive Interference: when one wave crest
overlaps a trough and they cancel each other out.
USES
noise canceling earmuffs
for pilots, jack hammers
Animation courtesy of Dr. Dan Russell, Kettering University

26. SHOW MOIRE PATTERNS

27. Standing Waves: when wave is reflected back
exactly opposite to the original wave
A = anti-node B = node
Animation courtesy of Dr. Dan Russell, Kettering University

28. Beats: periodic variation in loudness of sounds
caused when 2 slightly different frequencies are
sounded together
demo
Animation courtesy of Dr. Dan Russell, Kettering University
If one tuning fork vibrates at 264 Hertz, and the
other at 262 Hertz, then they are “in step” 2 times
each second. A beat frequency of 2 hz is heard.

29. THE DOPPLER EFFECT:
The Doppler effect is a change in frequency of a
wave due to the motion of the source or receiver.
Example: change in pitch of a car engine, horn or
siren as it passes you
As a sound wave approaches you, the pitch is
higher than normal because the waves
Come faster, at a higher frequency
After it passes, the sound waves are farther apart so
the sound is Lower

31. Doppler Effect occurs for visible light too.
Short lights waves are Blue and
Long wavelengths are Red
Astronomers can measure whether stars and galaxies are
moving toward us or away from us by looking at the
light shift.
 Blue Shift means - the light is coming faster –
stars are moving forward
Red Shift means- the star is going away
They can calculate the speed of a spinning star.
There is a blue shift on the side spinning toward us
and a red shift on the side spinning away.

32. Police use the Doppler effect of radar to determine
the speed of a car. A computer in the radar gun
compares the frequency of the radar emitted by
the antenna with the
frequency of the reflected waves.

33. OSCILLOSCOPE: A device that is used to measure
electrical signals as waves. It shows the strength of the
wave (amplitude) and the period of time between
each wave. You can then calculate the frequency
of the waves.