Vibration:

A vibration cannot exist in an instant

A wave is a vibration in

Waves move
Wave
and
from one position to another, not matter.
Ex: Light and sound
Sine wave:
Crest:
Trough:
Amplitude: The distance from the
to the crest or from the midpoint to the

The greatest vertical movement of the wave

SI unit: meters (m)
.
Wavelength:
•

How far until a wave repeats itself

Ex: crest to crest, trough to trough

SI unit: meters (m)
The energy transferred from a vibrating source is carried by a
, not by matter moving from one place to another.
–
Waves move
•
Energy carried by a wave consist of KE and PE
•
In a pendulum, the greatest KE is at
–
•
The greatest PE is at
–
•
This would be the middle (equilibrium line) of a sine wave
This would be the crest and trough of a sine wave
The
of wave remains the same
–
At the crests and troughs, there is the
–
At the middle, there is the most KE and the least PE

The time for a wave to repeat itself

SI Unit: seconds (s)…same as for time
and the
Period:
•
Period of a pendulum:

The time of a back and forth swing

The period depends ONLY on:
1. the length of the pendulum

A
2. the acceleration due to
pendulum has a longer period than a shorter pendulum.
.
Which will have a greater period, a pendulum with a 5 kg mass on 1 m of string or a pendulum with a 10 kg mass on 1
m of string?
Frequency:
•

# waves per second

Unit: Hertz (Hz) which means per second (1/s).
If the frequency of a vibrating object is known, its period can be calculated and vice-versa.

The frequency and period are

f = frequency
of each other.
f = 1/T
T = 1/f
Measured in

T = period
Measured in
What is the frequency in vibrations per second of a 100 Hz wave?
The Sears Building in Chicago sways back and forth at a frequency of about 0.1 Hz. What is the period of vibration?
Transverse wave:
The energy moves through the medium

Makes an “S” shape wave

Ex: light waves, string instrument
, but the motion of the wave is
Longitudinal wave:

Both the energy motion and the movement of the wave are

Makes a pulse through the wave

Ex: sound waves, earthquake waves
•
An
in a region at the same time.
•
There are 2 types of interference
.
.
pattern is formed by the overlapping of two or more waves that arrive
Principle of Superposition
Constructive interference:
The amplitude of the two original crests are combined to add to the new amplitude

Ex: A noisy room (several sound waves adding at the same time)
Destructive interference:
The amplitude of the original waves are subtracted because they are in opposite directions

Ex: anti-noise technology cancels out sound
Two waves reach the same place at the same time. One has an amplitude of 2 m up and the other has an amplitude
of 3 m up.
What type of interference is this?
What is the new amplitude?
Two waves reach the same place at the same time. One has an amplitude of 4 m up and the other has an amplitude
of 4 m down.
What type of interference is this?
What is the new amplitude?
Doppler effect:
The
the speed of the source, the greater the

•
•
will be.
Ex: the shift in pitch of a siren as it drives past you
The pitch of sound is
and
when the source moves
when the source moves
you,
you.
Pitch is the same as

As a source (like a siren) and a receiver (like you) move closer together, the pitch increases b/c the
frequency increases

As a source (like a siren) and a receiver (like you) move away from each other, the pitch decreases b/c
the frequency decreases
The Doppler Effect for Light
•
When the light source
when it
•
An increase in frequency is called a
or blue, end of the color spectrum.
because it is shifted toward the high frequency,
•
A decrease in frequency is called a
or red end, of the color spectrum.
because it is shifted toward the low-frequency,
Blue shift 
Red shift 
, there is an increase in its measured frequency, and
there is a decrease in its frequency.
When a source moves towards you, do you measure an increase or decrease in wave speed?
Does the pitch increase or decrease?
Does the frequency increase or decrease?