1. Chapter 13
Waves and Sound

2. What are Waves?
A wave is a periodic back and forth motion that transfers energy…
The substance through which a wave transfer energy is called the medium…

3. Waves and Energy Transfer
The back and forth motion is called oscillation…
When the wave travels through a medium the medium (or matter) does not travel with the wave…
Therefore, there is no net movement of the particles in the medium from one place to another..

4. Waves

5. Waves The high point of the wave is the crest
The low point of the wave is the trough
A series of waves is the wave train.

6. Types of Waves There are two major categories of waves:
1. Transverse Waves
2. Longitudinal Waves (sometimes called compression waves)

7. Transverse Waves
These are waves in which particles of the transmitting medium move back and forth at right angles to the direction in which the wave is traveling.
Waves traveling along a rope are transverse.
Light travels in transverse waves.

8. Longitudinal Waves
Waves in which the medium particles oscillate back and forth.
The particles compress as the wave travels through.

9. Longitudinal Waves
The compression is followed by a rarefaction pulse in which the particles spread out.

10. Wave Measurements Wave properties are described by four terms:
Wavelength: the distance from crest to crest
signified by the Greek letter lambda -
Amplitude: the height of the wave
Frequency: how often the wave passes a given point – expressed in Hertz (Hz)
Speed: the rate at which the wave travels

11. Speed of a Wave
The speed of a wave does not change as long as the medium remains constant.
Speed is directly proportional to both wavelength and frequency.
Equation for calculating speed of a wave:
Speed = wavelength X frequency (f)

12. Wave Behavior
Reflection
Refraction
Diffraction
Interference

13. Wave Behavior - Reflection
When a wave hits an obstacle or boundary, the wave “bounces” off the surface of the object in another direction.
The wave striking the boundary is the incident wave
The wave that bounces off is the reflected wave.
The Law of Reflection states that the angle of incidence is equal to the angle of reflection…
Or…the angles of the two waves are the same.
The imaginary line between the two waves is the “normal”.

14. Wave Behavior - Refraction
Waves travel at a certain velocity in specific mediums.
If the medium changes, the wave changes velocity.

15. Wave Behavior - Refraction
This change in velocity causes the wave to “bend”.
The bending path of a wave as a result of a change in wave speed is refraction.

16. Wave Behavior - Refraction
The bending path of a wave as a result of a change in wave speed is refraction.

17. Wave Behavior - Refraction
Waves always bend toward the medium that slows them down.

18. Wave Behavior - Diffraction
When a wave passes through a small barrier, it spreads out in all directions.

19. Wave Behavior - Diffraction
The spreading out of the wave is called diffraction.
When the opening is about the same as one wavelength, the wave spreads out most evenly.

20. Wave Behavior - Interference
Interference is the effect of combined waves upon the medium.
There are two types of wave interference:
1. constructive interference – when the crests of two waves or two troughs coincide – it creates a wave with higher amplitude
2. destructive interference – when the waves cancel each other out.

21. Sound Waves
Sound waves must have a medium to travel through in order to transfer energy…
There is no sound in the vacuum of space.
For humans audible sounds is a frequency range of 16 Hz – 20,000 Hz.
Sounds below what we can hear are infrasonic.
Sounds above what we can here are ultrasonic.

22. The Doppler Effect
When a wave source is in motion, the waves can “pile up” on each other and create a “new” sound…
This sound is a change in frequency…
An example of this is an ambulance speeding by…
This change in frequency is known as the Doppler Effect…

23. The Speed of Sound Sound waves travel slowly compared to light waves…
Under normal conditions, the speed of sound is about 340 m/s or 1116 ft/s or 761 mph…
There are two factors affecting the speed of sound in air…temperature and density…
Traveling faster than sound is called supersonic…
When an object moves faster than sound, constructive interference produces a shock wave in the form of a “sonic boom”