1. Vibrations and Waves

2. Vibration: a wiggle in time Wave: a wiggle in space and time. Cannot exist in one place, must extend from one place to another. http://www.stmary.ws/highschool/physics/home/vide os/wave2.html http://www.stmary.ws/highschool/physics/home/vide os/wave2.html Vibration of a pendulum The time a pendulum takes to swing to and fro does not depend on the mass of the pendulum. Period (T): time of a to-and-fro swing Depends only on the length (L) of the pendulum and the acceleration of gravity (g)

3. Wave description A sine curve is a pictorial representation of a wave. Crests: highpoint Troughs: low points Amplitude: distance from the midpoint to the crest or from the midpoint to the trough Wavelength: distance from the top of one crest to the top of the next one. Frequency (f): how frequently a vibration occurs. Unit: hertz (Hz) T= 1/f

4. Wave motion: sound and light are form of energy that travels in the form of waves. When energy is transferred by a wave, there is no transfer of matter. Speed of sound: 340 m/s Speed of radiant energy: (radio waves, microwaves, infrared, light, ultraviolet, x-rays, gamma) 3x10 8 m/s The energy transferred from a vibrating source to a receiver is carried by a disturbance in a medium, not from matter moving from one place to another within the medium. Wave speed Depends on the medium through which the wave travels. Wave speed = frequency x wavelength v= f x

5. Transverse wave: the motion of the medium is at right angles to the direction in which a wave travels. Fig 25-8 p356 Longitudinal wave: motion of the medium is along the direction of the wave. Fig 25-9 p357 YouTube - Transverse and Longitudinal Waves Interference: when waves overlap Constructive interference: when the crest of one wave overlaps the crest of another, their individual effects add together.

6. Destructive interference: when the crest of one wave overlaps the trough of another, there is a cancellation of their effects. Fig25-10 p358 Out of phase: when waves from two object arrive “out of step” In phase: when waves from two objects arrive “in step”. Standing waves Read p359

7. Doppler effect: the change of frequency due to the motion of the source. Read p361 Bow waves Read p363 Shock wavesRead p364 http://www.stmary.ws/highschool/physics/home/vide os/waves/dopplerv_14.mpg http://www.stmary.ws/highschool/physics/home/vide os/waves/dopplerv_14.mpg

8. 1) A nurse counts 76 heartbeats in one minute. What are the period and frequency of the heart’s occilations?

9. 2) Calculate the speed of waves in water that are 0.4m apart and have a frequency of 2 Hz.

10. 3) The lowest frequency we can hear is about 20 Hz. Calculate the wavelength associated with this frequency for sound that travels at 340 m/s.

11. 4) A monkey swings from a tree by his 0.30 m long tail. What is the period of swing of the monkey?

12. 5) Marla, a maid, is dusting a chandelier. As she is reaching up, she slips and grabs hold of the chandelier to catch her balance. When she lets go, the chandelier begins to swing with a period of 1.6s. How long is the cable connecting the chandelier to the ceiling?

13. Vibrations and Waves