1. Mechanical Waves & Sound
Chapter 17
Mechanical Waves & Sound

2. Waves
A repeating disturbance or movement that transfers energy through matter or space.
A wave will travel as long as it has energy.

3. Mechanical Waves
Mechanical Wave: is a disturbance in matter that carries energy from one place to another.
Mechanical waves require matter to travel
Medium: is a material (matter) that mechanical waves travel through solid liquid or gas.
Ex. Air, water, aluminum, copper,
The speed of mechanical waves changes with different mediums

4. Vibration: a repeating motion that follows a pattern
Mechanical wave is created when a source of energy causes a vibration to travel through a medium
Vibration: a repeating motion that follows a pattern
Sound is created by vibrations
Vocal cords

5. Longitudinal Transverse
There are 3 types of mechanical waves
Transverse waves
Longitudinal waves/ Compressional
Surface waves
Longitudinal Transverse

6. Up & Down, or Side to Side motion Draw a picture of a transverse wave
Transverse waves: is a wave that causes the medium to vibrate at right angles (perpendicular) to the direction in which the wave travels
Up & Down, or Side to Side motion
Draw a picture of a transverse wave
Ex.
Water
Rope
Slinky
Electromagnetic (radio waves, infrared, etc)

7. B. Transverse Waves Transverse Waves
medium moves perpendicular to the direction of wave motion

8. Crest: is the highest point above the resting position (top of the wave)
Trough: is the lowest point below the resting position (bottom of the wave)
Resting position: is the flat position of a wave before it starts moving
Slinky demo

9. B. Transverse Waves Wave Anatomy
corresponds to the amount of energy carried by the wave
wavelength
crests
amplitude
nodes
troughs

10. Longitudinal waves: is a wave in which the vibration of the medium travels parallel to the direction of the wave\
Slinky demo
Compression: a part of a longitudinal wave where the particles are pushed closely together
Rarefaction: a part of a longitudinal wave where the particles are spaced farther apart

11. C. Longitudinal Waves Longitudinal Waves (a.k.a. compressional)
medium moves in the same direction as wave motion

12. C. Longitudinal Waves Wave Anatomy
compression
wavelength
rarefaction
Amount of compression corresponds to amount of energy  AMPLITUDE.

13. Draw a longitudinal wave Ex. of longitudinal waves
Sound

14. Up & down movement like a transverse
Surface wave: is a wave that has characteristics of both transverse and longitudinal waves
Up & down movement like a transverse
Parallel movement of energy like longitudinal
Ex.
Ocean Waves
Earthquakes (waves through Earth’s surface)

15. Properties of Waves
Periodic Motion: is motion that follows a repeating pattern
Period: the time period for one interval of movement
Frequency: is the number of complete cycles that pass a point in a given amount of time
Frequency of waves are measured in hertz (Hz)

16. http://www. kettering. edu/physics/drussell/Demos/waves/wavemotion

17. Wavelength: is the distance of a complete cycle (either crest to crest or trough to trough)
Long wavelength = low frequency
Short wavelength = high frequency

18. D. Measuring Waves
Frequency ( f )
# of waves passing a point in 1 second
Hertz (Hz)
1 second
shorter wavelength = higher frequency = higher energy

19. v = wave λ × f D. Measuring Waves V:velocity (m/s) λ:wavelength (m)
Velocity ( v )
speed of a wave as it moves forward
depends on wave type and medium
V:velocity (m/s) λ:wavelength (m)
ƒ: frequency (Hz)
v = wave λ × f

20. D. Measuring Waves f λ v GIVEN: WORK: v = ? v = λ × f
EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.
GIVEN:
v = ?
λ= 3.2 m
f = 0.60 Hz
WORK:
v = λ × f
v = (3.2 m)(0.60 Hz)
v = 1.92 m/s λ v f

21. D. Measuring Waves f λ v GIVEN: WORK: λ = 417 m f = v ÷ λ
EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?
GIVEN:
λ = 417 m
v = 5000 m/s
f = ?
WORK:
f = v ÷ λ
f = (5000 m/s) ÷ (417 m)
f = 12 Hz λ v f

22. Wave Speed = wavelength X frequency
Wave speed changes in different mediums
If waves are traveling the same speed, then wavelength and frequency are INDIRECTLY related

23. Amplitude: is the distance from the resting position to either a crest or trough
Energy and amplitude are DIRECTLY related
High energy = high amplitude
Low energy = low amplitude
Amplitude in sound is called volume

24. Light waves travel faster than sound
Sound waves travel faster in liquids and solids than gas
Light waves travel faster in gases and vacuums than in liquids an solids.

25. Behavior of Waves
Reflection: is when a wave bounces off a surface it can not pass through
Reflection does not change the speed or frequency (the wave can be flipped upside down or side to side) Ex. Mirror
Law of Reflection: the angle of incidence (incoming wave) = the angle of reflection (outgoing wave)
All waves can be reflected
The reflection of sound is called an echo

26. reflection

27. Reflection terms
normal

28. Refraction: is the bending of a wave as it enters a new medium
Ex. light waves
Ruler in a beaker of water
Ex. sound waves
Listening to sound underwater

29. Diffraction: is the bending of a wave as is moves around an obstacle or passes through a narrow opening
Page 510
Eddy: is an area behind a mid-stream boulder where the water flows in a reverse direction (provides safety for rafters)
Chute: is an area of a river where the water is constricted to a narrow passage

30. defraction

31. Constructive Interference: is when 2 or more waves combine to form a wave with a larger displacement (amplitude)

32. Destructive interference: is when 2 or more waves combine to form a wave with a smaller displacement (amplitude) add together

33. Standing wave: is wave or waves that appear to stay in the same place
Plucking a guitar string
Waves in a river
Node: is the point on a standing wave where there is no displacement (amplitude)
Antinodes: are the crests and the troughs on a standing wave

34. 17.4 Sound Waves Sound waves are longitudinal waves
The speed of sound changes due to different types of mediums
Chart 514
Speed: is the distance traveled in a certain amount of time
Meters/second: m/s

35. Intensity: depends on the amplitude (volume) and the distance from the source
Decibels: (dB) is the unit for sound intensity
Chart on 515
Damage to ears around 120 dB

36. Frequency: is the number of wave cycles to pass a given point in one second
Measured in hertz (Hz)
Pitch: is the perceived frequency of sound
Different notes in music
All the different notes have a unique frequency

37. Ultrasound: use sound to locate objects or create pictures
SONAR, fish finders, radar
Animals use “echo-location”
Bats, dolphins, whales
Pregnant ladies get ultra sounds to check the baby’s health

38. Doppler Effect: pitch changes due to the object creating the sound moving closer or farther away
Pic on 516

39. Human Ear
Picture on 517
Outer ear: the collect and funnel the sound waves into the middle ear
Middle ear: amplifies the the vibrations
Inner ear: are where nerve endings receive and send the signal to the brain
The brain interprets those signals as sound

40. Resonance: waves of the same frequency combine (constructive interference)
amplifies the sound
Resonance can also cause to vibrate
Every object has a natural frequency, if a sound wave with the same frequency hits it, it will cause the object to vibrate

41. Seismic waves
Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.