1. Waves A repeating movement or disturbance that transfers energy...
…through matter
…or through space

2. Mechanical waves: waves that travel through a medium (some type of matter)
Two types:
Transverse wave: motion of matter in medium is perpendicular to the direction the wave is travelling
Wave travel
Water motion
Wavelength
(crest to crest)
Wavelength
(trough to trough)

3. Compressional wave: motion of matter in medium is in the same direction as the wave is travelling (Ex: sound)
Matter motion
Wave travel
rarefaction
compression

4. Wavelength
The wavelength of a wave is always the distance between matching points on a wave (Ex. Between two crests or between two compressions)
Slinky Lab

5. Period: the amount of time it takes one wavelength to pass a reference point. The units of a wavelength period are seconds (s).
One wavelength
What is the period of this wave?
360 s

6. Frequency: the number of wavelengths that pass a reference point in one second. The units of frequency are Hertz (Hz)
What’s the frequency of this wave?
It takes 360 s for one wave to complete its cycle
f = 1/(time for one cycle) = 1/period
= 1/(360 s)
= 3 x 10-3 Hz

7. What’s the period of this wave?
Period is 180 s
What’s the frequency of this wave?
f = 1 / period
= 1/(180 s)
= 6 x 10-3 Hz

8. Amplitude: the amount of energy in a wave increases as the height of the wave above its rest position (its amplitude) increases

10. Which wave has the greater energy?
The red one because it has the greater amplitude

11. Wave speed: How fast the wave is traveling through the medium
It’s possible to estimate how far away lightning has struck by counting the number of seconds between the flash and the arrival of the thunder.
It takes about 5 s for the sound of the thunder to travel one mile
Wave speed = 1 mile/5 s = 1700 m/5 s
= 340 m/s
The speed of sound in air is about 340 m/s

12. v = f λ Calculating wave speed: v f v = wave speed, units are m/s
f = frequency, units are Hz
λ = wavelength, units are meters (pronounced lambda)
Example:
1. A wave traveling in water has a frequency of 500 Hz and a wavelength of 3.0 m. What is the speed of the wave?
v = f λ
= (500 hz)(3.0 m)
= 1500 m/s
2. The lowest pitched sounds humans can hear have a frequency of Hz. What is the wavelength of these sound waves if their wave speed is 340 m/s? v
λ = v / f
= (340 m/s) / (20 Hz)
= 17 m f λ

13. The Behavior of Waves
Reflection: caused by waves striking an object and bouncing back off of it
Light wave
Echo = reflection of a sound wave

14. Surface normal: a perpendicular line to the reflecting surface
Angle of incidence: the angle between the arriving wave and the normal
Angle of reflection: the angle between the reflected wave and the normal
Law of reflection: The angle of incidence and the angle of reflection are equal

15. Refraction: a bending of the wave as it moves from one medium to another due to a change in wave speed.
Light travels more slowly in water than in air.
The light hitting and reflecting from the spoon underwater changes direction when it changes medium.
This makes the spoon look like it is bent.

16. Diffraction: the bending of waves around an object
The amount of diffraction that occurs depends upon the size of the obstacle or opening and the wavelength of the incident wave
Diffraction around a corner
Diffraction around an obstacle
Diffraction through an opening

17. + + What happens when two waves meet?
Crests and troughs line up: CONSTRUCTIVE INTERFERENCE
Crests and troughs don’t line up: DESTRUCTIVE
INTERFERENCE
Interference activity

18. Resonance: occurs when an object absorbs energy from vibrations that are at its natural frequencies
If one tuning fork is struck, its vibrations will cause the second one to start vibrating if they both resonate at the same frequency.

19. Chapter 11: Sound
Sound waves: Compressional waves that require some form of matter (solid, liquid or gas) for transmission
Outer ear gathers sound waves
Middle ear amplifies sound waves
Inner ear converts vibrations into nerve impulses

20. The speed of sound
Through which state of matter will sound travel the fastest? The slowest?
Because sound is a compressional wave, it travels fastest through solids because the particles are close together and can push against each other easily.
In a gas, the particles are very far apart and sound travels more slowly.
Sound does not travel at all in a vacuum (outer space).

21. Arrange materials in order of increasing sound transmission rates
Slow wave speed
Fast wave speed
Air
Water
Aluminum
Cork
Cork
Water
Brick
Brick
Aluminum
Air

22. Some numerical values:

23. Sound intensity
Recall that the amplitude (intensity) of a compressional wave depends upon how tightly packed the compressions are.
Rarefaction
Compression

24. The Decibel Scale: measures the intensity of a sound.
Units are decibels (dB)
The greater the intensity of a sound, the more energy is being transmitted by the wave.

25. Frequency and Pitch In which direction was the xylophone played?
The shorter the bar, the higher the pitch.
Shorter bar = shorter wavelength = higher frequency
The higher the frequency, the higher the pitch

26. Source moving toward observer.
Doppler Effect: a change in pitch due to motion of the source of the wave or of the observer.
Source moving away.
Sound wave expanded
= lower frequency
Source moving toward observer.
Sound wave compressed
= higher frequency
Siren emits at a constant 300 Hz

27. 1 2 Which way is the sound travelling? Toward the observer or away?