1. Chapter 25 Vibrations and Waves
Unit IV Sound and Light
Chapter 25
Vibrations and Waves

2. 25.1 Vibration of a Pendulum
A playground swing is a pendulum. Pendulums swing back and forth. Galileo discovered that the time of a pendulum swing does not depend on the mass of the pendulum or the angle of the swing!
T = time of swing
T = Period

3. Equation for a pendulum:
T = 2  (L/g)
T = Period
L = Length of Pendulum
g = acceleration due to gravity

4. Simple Harmonic Motion: back-and forth vibratory motion
25.2 Wave Description
Simple Harmonic Motion: back-and forth vibratory motion

5. SIMPLE HARMONIC MOTION
Sine Curve
The pattern traced out if a conveyor belt were pulled beneath a swinging pendulum. A sine wave represents transverse waves. In transverse waves the wave travels perpendicular to the medium.
SIMPLE HARMONIC MOTION

6. A wave is defined as: A disturbance in a medium.
25.3 Wave Motion
A wave is defined as: A disturbance in a medium.
When energy is transferred by a wave from a vibrating source to a distant receiver, there is no transfer of matter between the two points. ( The medium does not move!) Only the energy moves!

7. Motions of the wave is at right angles to the direction of the medium.
25.5 transverse waves
Motions of the wave is at right angles to the direction of the medium.
Waves on the stretched strings of musical instruments, electromagnetic waves, and “amber waves of grain” are examples.

8. Terms: Crest, Trough, Wavelength, Amplitude, frequency, node, antinode
Transverse Wave
Terms: Crest, Trough, Wavelength, Amplitude, frequency, node, antinode

9. Hertz-(kilohertz, megahertz, gigahertz)
Terms:
Crest Trough
Amplitude Wavelength
Frequency
Hertz-(kilohertz, megahertz, gigahertz)
Period
On the wave above to see the relationship between wavelength and frequency.

10. 25.6 Longitudinal Waves
Motion of the wave is parallel to the direction of the medium.
Sound Waves, is an example of a longitudinal wave.

11. Longitudinal Wave made from a guitar string.
Longitudinal Wave made from a guitar string.

12. 25.4 Wave Speed
The speed of a wave depends on the medium through which the wave moves.
Sound air: 330 m/s
Sound water: m/s
Sound travels faster in warm air and in more dense substances.

13. Calculating Wave Speed
V = velocity (m/s)
ƒ = frequency (hz)
 = wavelength (m)

14. Practice:
A wave vibrates 8 times each second and the length of the wave is 4 m. What is the frequency of the wave? What is the speed?
Answer: 8 hz
32 m/s

15. 25.7 Interference
Interference occurs when two waves share the same space at the same time.
Interference may be constructive or destructive.
Constructive: Reinforcement—Waves “In Phase”
Destructive: Cancellation—Waves “ Out of Phase”

19. 25.8 Standing Waves
A standing wave occurs when the incident and reflected waves interfere. Points out of phase are stationary and called nodes. Points in phase and producing high crests or troughs are called antinodes.

21. 25.9 The Doppler Effect
The apparent shift in frequency of a wave due to movement of either the observer or the source of the wave.
Examples: Police sirens, blue/red shifts in stars

22. Doppler Effect Demonstrations

23. Bow Waves
When the speed of the source in a medium is as great as the speed of the waves it produces, something interesting happens. The waves pile up. The crests pile up in a v shape, called a bow wave. This is an example of constructive interference.

24. 25.11 Shock Waves
A shock wave is a three dimensional wave produced when a supersonic craft passes through the air.
A sonic boom is heard when