1. Chapter 25 Vibrations and Waves

2. Vibration – a mechanical occillation around an equilibrium point
Wave - a progressive disturbance propagated from point to point in a medium or space without progress or advance by the points themselves, as in the transmission of sound or light.
For a pendulum, time it takes the pendulum arm to swing back and forth once is called the period. The period of a pendulum depends on the length of the pendulum arm and the acceleration of gravity.

3. Simple Harmonic Motion
The back-and-forth vibratory motion (often called oscillatory motion) of a swinging pendulum is called simple harmonic motion.

4. Wave Description: Crests – “high” points in a wave
Troughs – “low’ points in a wave
Wavelength – the distance between successive identical parts of a wave (ex. Distance from one wave crest to another wave crest).
Amplitude – the distance from the mid-point to the crest or trough
Frequency – how often a vibration occurs
Hertz – unit of frequency

6. Period =
frequency
Frequency =
period
What is the frequency in vibrations per second of a 100 Hz wave?
100 vibrations per second
2. The Sears Building in Chicago sways back and forth at a frequency of about .1 Hz. What is its period of vibration?
10 seconds

7. Wave Speed
Wave speed can be calculated by using the following equation:
wave speed = wavelength x frequency
or: ѵ = λ f
Example: A train passes by at a rate of 2 cars per second. Each train car is 10 meters long. How fast is the train moving?
V = (10 meters)(2 cars/sec)
V = 20 m/s

8. Wave Speed
The speed of a wave depends on the medium through which the wave moves.
Sound waves travel about 330 to 350 m/s in air depending on temperature
How fast does sound travel at room temperature? (25 C)
331 + (.6)(25)
346 m/s
v = 331 m/s + (0.6 m/s/C)•T

9. Wave Types
Transverse Wave – whenever the motion of the medium is at right angles to the direction which a wave travels, the wave is a transverse wave.
Longitudinal Wave – when the particles in a medium move back and forth in the same direction in which the wave travels.

10. Interference
If two rocks are dropped in a pond at the same time, they both produce waves in the water. These waves can overlap to produce an interference pattern.
If the crest of one wave overlaps the crest of another wave, the effects add together. This is constructive interference.
If the high part of one wave simply fills the low part of another wave, the effects cancel each other out. This is called destructive interference.