Wave Motion

1
Wave Motion

• WOD are underlined

2
Wave Motion

• WAVE A transfer of energy or propagation of a
  disturbance.
• A wave is the motion of a disturbance
• All waves carry energy and momentum.

3
Wave Motion

• A wave is the motion of a disturbance
• Mechanical waves require
• A medium that can be disturbed
• Some source of disturbance, i.e., a wave
  generator.
• All waves carry energy and momentum

4
Transverse Wave
Wave movement is perpendicular to wave
propagation. Wave is up and down motion.
5
Transverse
6
Longitudinal Wave or Compression Wave
Wave movement is parallel to wave propagation.
Demo with Colored Slinky.
7
To Prof On Next slide Show 1. Wave
Generator2. Fixed End3. Reflection4. Wave and
Reflection Add5. Molecules do not propagate, but
only oscilllate.
8
Longitudinal
9

• Waves do not move material.
• The medium the material that is waving. It
  only oscillates. It does not move forward along
  with the wave.
• MEDIUM DOES NOT MOVE FORWARD.
• It stays in place and oscillates.
• Note the blue bobber in the next slide.

10
Surface waves
11

• By watching the blue bobber oscillate, it can be
  seen that a surface wave is a combination of a
  transverse wave (up and down) and a longitudinal
  wave (left and right) which produces a SHM in the
  shape of a circle.

12
Parts of a wave. They repeat.
13
1 wave
Ending Node is Starting Node for the next wave.
14
Waveform A Picture of a Wave

• The brown curve is a snapshot of the wave at
  some instant in time
• The blue curve is later in time
• The high points are crests of the wave
• The low points are troughs of the wave

15
Wave Parts

• Crests high points
• Troughs low points
• Nodes Zeros or Intercepts

16
New Symbol

• Wavelength ? Lambda
• The length of the wave
• Distance between identical points on adjacent
  periods, i.e., crest to crest, trough to trough,
  or starting node to starting node.
• Measured in meters
• Or micrometers or nanometers

17
In the drawing, one cycle is shaded in color.
The amplitude A is the maximum excursion of a
particle of the medium from the particles
undisturbed position. The wavelength is the
horizontal length of one cycle of the wave. The
period is the time required for one complete
cycle. The frequency is related to the period
and has units of Hz, or s-1.
18
Velocity of a wave

• Remember
• ? distance per cycle
• f cycles per time
• Multiply them together
• ?f distance/cycle cycles/time

19
Velocity of a wave

• Remember
• ? distance per cycle
• f cycles per time
• Multiply them together
• ?f distance/cycle cycles/time
• ?f distance/time velocity
• Velocity of wave v f ?

20
Velocity of a wave

• The velocity of a wave is determined entirely by
  the medium.
• The frequency of a wave is determined entirely by
  the source (wave generator).
• The wavelength, ? v/f

21
Velocity of a wave

• The velocity of a wave is determined entirely by
  the medium.
• i.e.,
• Sound travels at different speeds through water,
  air, and wood.

22
Problem

• A Helium-Neon laser has a wavelength of 6.33
  10-7 m, and a frequency of 4.74 10 14 Hz.
  Find the velocity of this laser beam.

23
Problem

• A Helium-Neon laser has a wavelength of 6.33
  10-7 m, and a frequency of 4.74 10 14 Hz.
  Find the velocity of this laser beam.
• v f ? 4.74 10 14 Hz 6.33 10-7 m

24
As a sine wave

• A transverse wave can easily be viewed as a sine
  wave

25
Longitudinal waves can too.
26
Density is a sine wave
Areas of high density are called Compressions. Ar
eas of low density are called Rarefactions.
Note The speaker causes compressions in the
air, which you ear interprets as sound.
27
Interference of Waves
28
Interference of Waves

• Two traveling waves can meet and pass through
  each other without being destroyed or even
  altered
• Waves obey the Superposition Principle
• Superposition Principle states the resulting wave
  is found by adding together the displacements of
  the individual waves point by point

29
Whats going to happen?

• Two wave move towards each other

30
They add up on top of each other

• They add up on top of each other

31
Afterwards

• The two waves disturbances have no lasting effect
  on each other

32
Whats going to happen?

• Two wave move towards each other

33
They add up on top of each other

• They add up on top of each other

34
Afterwards

• The two waves disturbances have no lasting effect
  on each other

35
Constructive Interference

• Two waves, a and b, have the same frequency.
• Are in phase
• The combined wave, c, has the same frequency and
  a greater amplitude.

36
Destructive Interference

• Two waves, a and b, have the same amplitude and
  frequency
• They are half a cycle out of phase
• When they combine, the waveforms cancel
• Wave of same f, out of phase, cancel each other.

37
Reflection of Waves Fixed End

• Whenever a traveling wave reaches a boundary,
  some or all of the wave is reflected

38
Reflection of Waves Fixed End

• Whenever a traveling wave reaches a boundary,
  some or all of the wave is reflected
• When it is reflected from a fixed end, the wave
  is inverted.
• The shape remains the same, just upside down.

39
What happens when a wave interferes with its own
reflection?

• Sometimes we get standing waves.

40
(No Transcript)
41

• The a string will only allow certain wavelengths
  to be standing waves because the endpoints need
  to be nodes,
• i.e., the length of the string determines the
  wavelength for harmonics.
• For a string with two fixed ends,
• ? 2L / n n 1, 2, 3, 4 .