1. Chapter 25: Vibrations and Waves

2. What is a wiggle in time called?
A vibration

3. What is a wiggle in space and time called?
A wave

4. Vibration of a Pendulum
The time for one complete forward and back swing is called the period.

5. Simple Harmonic Motion
Back and forth vibratory motion of a pendulum
Pendulum bob filled with sand (Oppenheimer, page 373)

6. Calculating the Period
frequency

7. Wave Description
Sine curve

8. Parts of a Wave

9. Frequency of a Wave How frequent or how often a vibration occurs
Measured in cycles/second or Hertz (Hz)
1-cycle/second = 1-Hz
frequency = 1
period

10. What is the frequency in Hz of a wave vibrating at 75-cycles/second?

11. AM and FM Radio Frequencies
AM = kilohertz kilo = 1,000
FM = megahertz mega = 1 million

12. Wave Speed wave speed = wavelength x frequency
What is the speed of a wave that has a wavelength of 2 meters and a frequency of
4 Hz?
8 m/s

13. Wave Speed (cont’d)
Light waves travel much faster than sound waves 300,000,000 m/s
Sound waves = 340 m/s (average)

14. Wave Motion
When energy is transferred by a wave from a vibrating source to a distant receiver, there is no movement of matter between the two points.
To put it simply, only the disturbance/energy is transferred, not the medium (stuff).

15. Transverse Waves
Medium moves at right angles to the direction in which the wave travels
Ocean, Light (electromagnetic waves)

16. Longitudinal Waves
Medium moves parallel (same direction) to the direction in which the wave travels.
Sound waves

17. Interference of Waves
Occurs when two waves are at the same place at the same time
Two types of interference:
Constructive Interference
Destructive Interference

18. Constructive Interference
Occurs when waves are in phase
Crest + Crest or Trough + Trough
Amplitude increases

19. Constructive Interference

20. Destructive Interference

21. Standing Waves Standing waves are caused by interference
They appear to be “standing still”
Reflected wave interferes with the incoming wave and they’re in phase

22. A Standing Wave

23. Standing Waves
The high points are called antinodes. They’re caused by constructive interference.
The low points are called nodes and they’re caused by destructive interference.

24. The Doppler Effect
Movement is needed, either the source of the sound or the observer.
Frequency/pitch increases as the source gets closer to you and it decreases when the source moves away.

26. Bow Waves and Shock Waves

27. Bow Waves Two-dimensional
Produced by a boat (bug, etc.) when it’s moving faster than the waves it’s producing.

28. Shock Waves Three-dimensional cone
Results in a sonic boom due to high pressure