PAGE EDITORS: Marcelo Norcini, Andrea Wenrich, Alexa Kalandiak

Natland Note: (8/18/13) This is where I will post comments about suggested and necessary improvements to your page as you complete it while we are going over the content for your topic. Keep an eye on this note, as I will post new ones from time to time.


Waves and Sound video
(email me if you have any issue watching it. Remember to take notes on the video as content discussed will NOT be covered formally in class as well).

The nature of waves
  • A wave is a traveling disturbance
  • A wave carries energy from place to place
Mechanical Waves
  • require a medium to propagate
Non- Mechanical Waves
  • do no require a medium to propagate
Longitudinal Waves
  • particle motion is in the same direction as the waves motion (direction of propagation)
Transverse Waves
  • particle motion is perpendicular to the direction of the wave propagated


- sound
- slinky
- rope, tightly coiled slinky
- "The Wave"
- light

  • Wavelength = meters
  • Speed of light = 3.08*10^8 meters per second (C)
  • Period = seconds
  • Frequency = 1/seconds= Hz
  • Amplitude = meters

Properties of the Speed of Sound
  • The speed of sound is faster in a solid than in a liquid and faster in a liquid than in a gas. Solid > Liquid > Gas
  • The smaller/lighter the mass of the molecule (in gases) the faster the speed of sound.
  • The higher the temperature the faster the speed of sound because the molecules travel faster when temperature ries

Speed of a Wave
  • determined by the medium traveled through
  • V=wavelength/period= λf
  • Speed of wave on string=√(T/u) where T= tension of a string and u=linear mass density
  • An object will vibrate at its natural frequency

Principle of Super Position
  • positive amplitude= molecules more compressed, dense
  • speed of sound wave in air is the same for all notes and frequencies, only the wavelength changes

Two Speakers Producing the Same Sound
  • Δd=d2-d1=path difference between the two sound wave
  • Constructive Interference in phase: Δd=nλ
  • Destructive Interference in phase: Δd=(n+1/2)λ
  • Constructive Interference: When the troughs and peaks of a wave line up to produce an amplified sound
  • Destructive Interference: When the trough of a wave meets with the peak of another wave, sounds cancels out
  • Out of phase: half a cycle off, equations for constructive interference and destructive interference are the same except switched


World War I acoustic mirror in Kilnsea, East Yorkshire, UK. Concrete mirrors like these were constructed before the invention of radar to detect the sound of approaching enemy aircraft.
World War I acoustic mirror in Kilnsea, East Yorkshire, UK. Concrete mirrors like these were constructed before the invention of radar to detect the sound of approaching enemy aircraft.

Components of a Wave

Transverse versus Longitudinal Waves
Transverse versus Longitudinal Waves

Wave Interference - Constructive versus Destructive

This image shows two out of phase waves. The red wave is exactly 180 degrees out of phase with the blue wave.

Fork Vibrations


1. A sound wave has a frequency of 262 Hz. What is the time between successive wave crests?

Period = 1/ Frequency

Period = 1 / 262 Hz

Period = .0038s

2. A sound wave produced by a clock chime 515 m away is heard 1.50 s later. The frequency of the sound is 436 Hz.

(a) What is the speed of sound in air?
(b) What is the period of the sound wave?
(c) What is its wavelength?

(a) Velocity = delta distance / delta time
Velocity = 515m / 1.50s = 343.3 m/s

(b) Period = 1 / Frequency
Period = 1 / 436 Hz
Period = .00229s

(c) Velocity = Wavelength * Frequency
Velocity / Frequency = Wavelength
343.3 m/s / 436 Hz = .7874 m

3. Suppose that the two speakers in Figure 17.7 are separated by 3.20 m and are vibrating exactly out of phase at a frequency of 429 Hz. The speed of sound is 343 m/s. Does the observer at C observe constructive or destructive interference when his distance from speaker B is 2.40 m ?

Screen Shot 2014-05-03 at 1.11.02 AM.png
Figure 17.7

  1. The Δd would can be found by finding the difference between the AC and BC.
  2. BC and AB are given and it can be seen in the picture that angle ABC is 90 degrees.
  3. AC can be found using the pythagorean theorem.
  4. AB^2 + BC^2 = AC^2
  5. AC = 4
  6. Δd = 4m - 2.4m = 1.6m
  7. Now we need to find the wavelength
  8. Velocity = Wavelength * Frequency
  9. Wavelength = Velocity / Frequency = .800m
  10. (Δd/λ) - .5 will determine whether or not the there is constructive or destructive interference.
  11. (1.6m/.800m) - .5 = 1.5 There is destructive interference.

OTHER PROBLEMS (without solutions):


A good video depicting the motions of a sound wave and other important qualities of a sound wave is the following:

Website with good description and animation of constructive and destructive interference