1. Waves and Sound
Feel the Beat….

2. Mechanical Waves Require a medium to travel.
Transverse, Longitudinal, Surface

3. Wave Description Frequency Unit Equation
How frequently a wave pulse occurs.
Unit
Hertz (Hz)
1 Hz = 1/seconds or s-1
Equation

4. Wave Description Period Equation
The time (in seconds) that it takes for one wave to pass.
Equation
T = Period (in seconds)

5. Wave Description
Frequency and Period are Inversely Related

6. Types of Waves Transverse Waves
Matter moves perpendicular to the direction of wave movement.

7. Types of Waves Longitudinal Waves
Matter moves parallel to the direction of wave movement.

8. In the standing wave shown, what is the amplitude?
In the standing wave shown, what is its wavelength?
In the standing wave shown, how many nodes are there?

9. Key Principles
Transverse wave particles vibrate perpendicular to the wave direction and longitudinal wave particles vibrate parallel to the direction of the wave propagation.
Sound waves are mechanical longitudinal waves. Light waves are electromagnetic transverse waves.
The speed of a wave depends only on the properties of the medium.
The energy of a wave is directly proportional to the square of the amplitude.
Superposition Principle: When two or more waves exist simultaneously in the same medium, the resultant amplitude at any point is the algebraic sum of the amplitudes of each wave.

10. Key Formulas

11. Wave Encounters When a wave meets an object 4 things could happen
Reflection – wave bounces in new direction
Refraction – wave bends as it passes thru
Diffraction – wave bends as it passes around
Absorption – wave is absorbed and disappears

12. Superposition Principle
Constructive vs destructive
Moving waves allow for this to change as the wave moves

13. Key Principles - Sound
The speed of a wave depends only on the properties of the medium.
The intensity of sound is inversely proportional to the distance.
The harmonics produced in open pipes are similar to those produced in strings.
The fundamental occurs when the length of the pipe (or string) equals 1/2 λ.
The fundamental on a closed pipe occurs when the length of the pipe equals 1/4 λ. Only the odd harmonics are possible for a closed pipe.
Whenever two waves exist simultaneously in the same medium and they are nearly at the same frequency, beats are set up.
Doppler effect is the apparent change in frequency of a source of sound when there is relative motion of the source and the listener.

14. Key Formulas

15. vsolids > vliquids > vgases
Wave Speed
Speed of sound is determined only by the medium it travels through.
The closer the molecules are, the faster it travels.
Sound travels fastest through solid
vsolids > vliquids > vgases
Slower than sound is subsonic
Faster than sound is supersonic
Material
Sound Speed
Air
330
Helium
965
Water
1530
Wood
2000
Gold
3240
Steel
5940

16. Sound Wave Properties Pitch is determined by frequency
Most sound waves have multiple frequencies – timbre
Energy determines loudness of the sound
Intensity decreases as the wave moves away from the source
Loudness measured in decibels

17. Intensity Scales Examples
Hearing threshhold 0 dB
Whisper 20 dB 102X
Ordinary talk 60 dB X
Jackhammer 90 dB X
IPOD Maxed dB X
Front Row Concert 110 dB X
Pain Threshold 130 dB 1013X

18. Doppler Effect Effect of moving objects and sound waves
Sound waves get closer together as the source approaches
Sound waves spread out as the source goes away

19. Resonance Every wave has a natural frequency
Constructive interference increases energy causing resonance
Increased amplitude = increased energy

20. Harmonics
Almost all sounds are a mix of various frequencies – harmonics. Different mixes can produce the same overall frequency but a slightly different sound….

21. Developing the harmony

22. Creating a sound…