1. Waves and Sound

2. Waves A wave is any disturbance that travels away from its source.
We will study only mechanical waves traveling through a medium.
Disturb particles from their equilibrium position as the wave passes
Particles return to equilibrium position once the wave has passed

3. Energy Transport
Waves can transport energy from one place to another, without transporting matter.

4. Wavespeed
The speed that a wave travels through a medium depends on the mass of the medium.
More massive medium = slower speed
Less massive medium = faster speed
v = λf

5. Types of Waves Transverse Waves Longitudinal Waves
Particles in medium move perpendicular to wave
Described in terms of amplitude, wavelength, peak, trough, and frequency
Longitudinal Waves
Particles in medium move along same line as wave
Described in terms of wavelength, compressions and rarefraction

8. Periodic Waves Periodic waves repeat the same pattern over and over.
Classified by:
Period
Time it takes for a pattern to repeat itself
Wavelength
Distance from one wave to the next
Frequency
How often a pattern repeats itself

9. Harmonic Waves
Harmonic waves are a special kind of wave in which the disturbance looks like a sine or cosine function

10. Superposition Traveling waves obey the principle of superposition.
When two or more waves meet (or overlap) the net disturbance is the sum of the two individual disturbances
Once the waves have passed, they return to their original shape and size.
Also called interference.

12. Superposition of Harmonic Waves

13. Reflection
When mechanical waves encounter an abrupt boundary, part of the wave reflects.
Reflected waves can be inverted or upright
Their orientation depends on what medium it encounters.
If the wave goes from a more dense medium to a less dense medium, the wave is upright.
If the wave goes from a less dense medium to a more dense medium, the wave is inverted.

14. Going from a less dense string to a more dense string
Going from a more dense string to a less dense string

15. Special Cases
If the second medium is infinitely massive (or infinitely light) the wave experiences total reflection.

16. Standing Waves
A special case when a wave is reflected and the reflected wave interferes with the incident wave so that the wave appears not to move.
The points where standing waves meet are called nodes.
The points where standing waves are furthest apart are called antinodes.

17. Standing waves

18. Sound
A sound wave is a longitudinal wave that can be recognized by our ears.
The audible range is generally from 20Hz to 20kHz.
The speed of sound is approximately 331 m/s for 00C and 343 m/s for room temperature.
Sound must have a medium to travel through.

19. Sound Sound acts like a longitudinal wave.
Like other waves, its speed depends on its medium.
More restoring force = faster waves
More inertia = slower waves
Speed of sound also depends on temperature
Warmer medium = faster waves

20. Standing Waves
When air moving through a pipe makes a standing wave, it produces a note.
Like waves on a string, the standing waves are made only at certain (natural) frequencies and have certain wavelengths.

21. Open and Closed Pipes For pipe open at both ends (n = 1, 2, 3, 4…)
λ = 2L/n
F = nv/2L
For pipe open at one end (n = 1, 3, 5, 7…)
λ = 4L/n
F = nv/4L

22. Beats
When sound of two different frequencies are played at the same time, the waves interfere creating beats.

23. Doppler Effect http://youtu.be/Tn35SB1_NYI
An apparent change in frequency due to relative motion between the source and the observer.