1. What causes mechanical waves?
List four different examples of mechanical waves (just think of waves).
Bring Digital Cameras

2. Mechanical Waves and Sound
Chapter 17
Mechanical Waves and Sound
SPS9 Students will investigate the properties of waves
Recognize that all waves transfer energy
Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves.
Relate the speed of sound to different mediums.
Explain the Doppler Effect in terms of everyday interactions.

3. 17.1 Mechanical Waves What causes mechanical waves?
What are the three main types of mechanical waves?

4. 17.1 Mechanical Waves
What causes mechanical waves?
Mechanical wave – disturbance in matter that carries energy from one place to another
Medium – material that a mechanical wave travels through
Required
A source of energy must cause a vibration in the medium

5. 17.1 Mechanical Waves
What are the three main types of mechanical waves?
Mechanical waves are classified by how they move through a medium

6. 17.1 Mechanical Waves
What are the three main types of mechanical waves?
Transverse Wave - the medium vibrates perpendicular to the direction the energy is going
Part
Crest – highest point
Trough – lowest point
Equilibrium – resting point (when there is no wave)
Amplitude – the distance from equilibrium to crest or trough
Wavelength – distance from one point to the same point on the next wave

7. 17.1 Mechanical Waves
What are the three main types of mechanical waves?
Longitudinal Wave – vibration is parallel to the direction the energy flows
Parts
Compression – particles are the closest together
Rarefaction – particles are the farthest apart
Wavelength – the distance from one point on a wave to the same point on another

8. 17.1 Mechanical Waves
What are the three main types of mechanical waves?
Surface Wave – travels along the boundary between two mediums
Circular motion of the particles
Combines actions of longitudinal and transverse waves

9. 17.2 Properties of Mech. Waves
What determines the frequency of a wave?
How are frequency, wavelength, and speed related?
How is the amplitude of a wave related to the wave’s energy?

10. 17.2 Properties of Mech. Waves
How are frequency, wavelength, and speed related?
Period – the time for one complete cycle
Frequency – the number of complete cycles per second
Measured in hertz (Hz)
Determined by how fast the source of the wave vibrates

11. 17.2 Properties of Mech. Waves
What determines the frequency of a wave?
Wavelength – distance from one point on a wave to the same point on the next wave
Wave Speed – how fast energy is transferred by a wave
Sound 345 m/s
Light 300,000,000 m/s

12. 17.2 Properties of Mech. Waves
How are frequency, speed and wavelength related?
The wave equation
v = speed of the wave (m/s)
f = frequency (Hz)
l = wavelength (m)
Frequency and wavelength are inversely proportion
When one increases, the other decreases
v=fl

13. 17.2 Properties of Mech. Waves
What determines the frequency of a wave?
Practice problem 1
A wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave?
Variables?
Fill in the equation?
Answer?
v=(2.0Hz)(2.0m)
v=4 m/s
v=fl
l = 2.0 m
f = 2.0 Hz

14. 17.2 Properties of Mech. Waves
What determines the frequency of a wave?
Practice problem 2
What is the wavelength of an earthquake wave if it has a speed of 5 m/s and a frequency of 10 Hz?
Variables?
Fill in the equation?
Answer?
5 m/s=(10 Hz)l
l=0.5 m
v=fl
v = 5 m/s
f = 10 Hz

15. S-51
What determines the frequency of a wave?
A sound wave with a speed of 345 m/s has a wavelength of 25 m. What is the frequency of the wave?

16. S-52
What determines the frequency of a wave?
A wave of light has a speed of 300,000,000 m/s. What is the wavelength of a wave with a frequency of 450,000,000 Hz?

17. 17.2 Properties of Mech. Waves
How is the amplitude of a wave related to the waves energy?
Amplitude – the maximum displacement from the rest position
Amplitude is directly related to energy
Larger amplitude means more energy
Think of a tidal wave
A really huge wave does much more damage than a small wave

18. 17.3 Behavior of Waves How does reflection change a wave?
What causes the refraction of a wave when it enters a new medium?
What are two types of interference?

19. 17.3 Behavior of Waves
How does reflection change a wave?
Reflection – when a wave bounces off a boundary between mediums
Does not change the speed of a wave
Does not change the frequency of a wave
Can be flipped upside down

20. 17.3 Behavior of Waves
What causes the refraction of a wave when it enters a new medium?
Refraction – the bending of a wave as it enters a new medium
Because one side of the wave moves slower than the other
Slows down, angle becomes smaller
Speeds up, angle becomes greater

21. 17.3 Behavior of Waves
What are two types of interference?
Interference – when two or more waves overlap and combine
Constructive – the waves combine to make a greater amplitude
Destructive – the waves combine to make a smaller amplitude
Graphically – add the amplitudes together
Above equilibrium is positive
Below equilibrium is negative

22. 17.3 Behavior of Waves
What are two types of interference?

23. S-53
What are two types of interference?
Draw a wave that has a wavelength of 6 squares, and an amplitude of 4 squares.
If it went through constructive interference with an identical wave, what would be the maximum amplitude reached?

24. S-54 What is refraction? Where does refraction occur?
What causes the refraction of a wave when it enters a new medium?
What is refraction?
Where does refraction occur?
Give one example of refraction.

25. 17.4 sound and Hearing What properties explain the behavior of sound?
How does the frequency of a sound change for a moving source?
What are the functions of the three main regions of the ear?

26. 17.4 Sound and Hearing Intensity – the rate of energy flow
What properties explain the behavior of sound?
Intensity – the rate of energy flow
Increases with the energy of the source
Decreases rapidly with distance from source
Measured in decibels (db)
Interpreted as Loudness
Subjective – subject to a persons interpretation

27. 17.4 Sound and Hearing Frequency Interpreted as Pitch
What properties explain the behavior of sound?
Frequency
Interpreted as Pitch
High frequency – high pitch
Low frequency – low pitch
Depends some on age and health

28. 17.4 Sound and Hearing
How does frequency of sound change for a moving source?
Doppler effect – a change in frequency caused by motion of the sound source, listener, or both.
Approaching sounds are higher in frequency
As the source moves away sounds are lower in frequency

29. 17.4 Sound and Hearing Three main regions of the ear
What are the functions of the three main regions of the ear?
Three main regions of the ear
Outer ear (external ear, ear canal, ear drum)
Gathers and focuses sound
Middle ear (3 bones – hammer, anvil, stirrup)
Receives and amplifies vibrations
Inner ear (cochlea)
Nerves sense vibrations and send signal to brain

30. S-54 Name the three main parts of the ear and their functions.
What are the functions of the three main regions of the ear??
Name the three main parts of the ear and their functions.

31. S-55 What is the Doppler Effect? Give one example.
How does frequency of sound change for a moving source?
What is the Doppler Effect?
Give one example.

32. S-56
Wet Cat!
Test Day!
Yah!