1. Chapter 17: Mechanical Waves & Sound

2. 17.1 Mechanical Waves
P4.4A Describe mechanical waves in terms of wavelength, amplitude, frequency, and speed.
P4.4B Identify everyday examples of transverse and compression (longitudinal) waves.
P4.4C Compare and contrast transverse and compression (longitudinal) waves in terms of wavelength, amplitude, and frequency.

3. What are Mechanical Waves?
Mechanical waves- disturbance in matter that carries energy from one place to another.
Requires matter to travel through, this material is called a medium.
Medium can be solids, liquids, and gases.
Ex: Wave pool- water is the medium.

4. Three types of Mechanical Waves
Transverse
Longitudinal
Surface

5. Transverse Waves AKA: Secondary (S) waves
Carries energy from left to right, in a direction perpendicular to the up and down motion of the rope.
Travel through solids- move slow, but carries energy.
Ex: seismic wave (earthquake waves)
Crest- highest point of the wave above the rest position.
Trough-lowest point below the rest position.

6. Transverse Waves

7. Longitudinal Waves AKA: primary (p) waves
Wave in which the vibration of the medium is parallel to the direction the wave travels.
Faster than transverse waves and can move through liquids and solids.
Compression- an area in where the particles in a medium are spaced close together.
Rarefaction- an area where the particles in a medium are spaced out.

8. Longitudinal Wave
Ex: sound waves & earthquake waves

9. Surface Waves
A wave that travels along the surface.
Ex: ocean waves

10. 17.2 Properties of Mechanical waves

11. Frequency and Period Period: the time required for one complete cycle.
Frequency: number of complete cycles in a given time.
hertz (hz): cycles per second (how frequency is measured)
A waves frequency equals the frequency of the vibrating source producing the wave.

12. Frequency

13. Wavelength
Distance from one crest to the next crest, or one trough to the next trough.

14. Wavelength
Increasing the frequency of a wave decreases its wavelength.

15. Wave Speed Speed = wavelength X frequency
Speed of a wave can change if it enters a new medium or if pressure and temperature changes.

16. Amplitude Distance from the resting position to the crest of the wave.
The more energy a wave has the greater the amplitude.

17. 17.3 Behavior of Waves

18. Reflection
Occurs when a wave bounces off a surface that it cannot pass through.
The wave is flipped upside down.
Reflection does not change the speed or frequency.

19. Refraction Bending of a wave when it enters a new medium.
When a wave enters a medium at an angle, one side of the wave moves slower than the other side.
Ex: waves approaching shore

20. Diffraction
Bending of a wave as it bends around an obstacle or passes through a narrow opening.
If the wavelength is small the diffraction will be small. If the wavelength is large the diffraction is large.

21. Diffraction

22. Interference
Interference occurs when two or more waves overlap and combine together.
Two types of interference are:
1) constructive interference and
2) destructive interference.

23. Constructive Interference
Occurs when two or more waves combine to produce a wave with a larger displacement.
The combined wave will have a larger trough and crest.

24. Destructive Interference
Occurs when two or more waves combine to produce a wave with a smaller displacement.
Produces a wave with a reduced amplitude.

25. Standing Waves
Standing wave is a wave that appears to stay in one place- it does not seem to move through the medium.
Ex: plucking a guitar string
Node: point on a standing wave that has no displacement.
Antinode: point where a crest or trough occurs midway between two nodes.

26. Standing Waves

27. 17.4 Sound and Hearing

28. Properties of Sound Waves
Sound waves are longitudinal-compressions & rarefactions that travel through a medium.
Many behaviors of sound can be explained using a few properties:
Speed
Intensity and loudness
frequency and pitch

29. Speed Speed of sound is 342 meters per second.
Sound waves travel faster in solids, slower in liquids and slowest in gases.
Speed of sound depends on density of medium and how elastic the medium is.

30. Intensity and Loudness
Intensity is the rate at which a wave’s energy flows through a given area.
Depends on the wave’s amplitude and distance from the source.
Sound intensity levels are measured in units called decibels.
Loudness is a physical response to the intensity of a sound (subjective).
As intensity increases, loudness increases.

31. Frequency and Pitch
Pitch is the frequency of a sound as you perceive it.
Pitch depends on frequency.
High-frequency sounds have a high pitch, and low frequency sounds have a low pitch.
Pitch also depends on a person’s age and the health of their ears.

32. The Doppler Effect
Change in sound frequency caused by motion of the sound source, motion of the listener, or both.
As a source of sound approaches , an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency.
Ex: siren on ambulance