CONCEPTUAL PHYSICSVibrations and Waves

Vibration: a wiggle in timeWave: 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/videos/wave2.html

Vibration of a pendulumThe 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)

g

LT 2

Wave descriptionA sine curve is a pictorial representation of a

wave.Crests: highpoint Troughs: low pointsAmplitude: distance from the midpoint to the

crest or from the midpoint to the troughWavelength: 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

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/sSpeed of radiant energy: (radio waves,

microwaves, infrared, light, ultraviolet, x-rays, gamma) 3x108 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 speedDepends on the medium through which the wave

travels.Wave speed = frequency x wavelength

v= f x

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 WavesInterference: when waves overlap

Constructive interference: when the crest of one wave overlaps the crest of another, their individual effects add together.

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

Doppler effect: the change of frequency due to the motion of the source. Read p361

Bow waves Read p363Shock waves Read p364http://www.stmary.ws/highschool/physics/hom

e/videos/waves/dopplerv_14.mpg

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

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

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.

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

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?

CONCEPTUAL PHYSICSVibrations and Waves