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Chapter 25 Vibrations and Waves

Chapter 25 Vibrations and Waves. 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.

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Chapter 25 Vibrations and Waves

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  1. Chapter 25Vibrations 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

  5. Period = 1 frequency Frequency = 1 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

  6. 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

  7. 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

  8. 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.

  9. 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.

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