Motion and terms

Wave Motion

Wave motion is defined as the movement or a distortion of a material or medium, where the individual parts or elements of the material only move back-and-forth, up-and-down, or in a cyclical pattern.

Examples:

Wave in ballgame

At the ballgame, someone in the stands may start up a "wave" by standing up and then sitting down. The people on one side then stand up and sit down, then the next people, and so one.

Everyone is still in their seats, but the wave traveled through the ballpark from one end to the other.

Rope or string

You can shake a rope, causing a wave motion. The parts of the rope only move up-and-down, but the wave moves from one end of the rope to the other. A guitar string also has this type of motion.

Vibrating string demonstrates waveform

Types of Waves

A Transverse wave is one where the direction of vibrations of particles is at right angle to the direction of the wave. Eg. Water waves, waves on spring or electromagnetic waves example light.

A Longitudinal wave is one where the direction of vibration of particles is parallel to the direction of the wave. Eg. sound, displacing the particles of a spring parallel to its length

A pulse is a single disturbance that moves through a medium from one point to the next point (as shown below.

Graphs

Distance / time graph

The graph below represents a distance / time graph for a single particle as it oscillates in a wave

Displacement / distance graph

The following is a displacement-distance graph shows the displacement from the undisturbed position, at a certain time, of the particles vibrating at different distances from the source in the transmitting medium

Wave Terms

a Amplitude: the is the maximum displacement of a particle in the wave

λ Wave Length: the distance between successive troughs or crest

crest -this is the furthest point the particle can reach in a positive direction

trough- this is furthest point the particle can reach in a negative direction

T Period: The time for one complete oscillation of a particle of the wave. It is measured in seconds. One complete oscillation can be found by following the dotted line in the graph. The particle moves from point W through to X, then to Y, then to Z and back to W, its initial position. The period for the wave above is 0.1 s

f Frequency: the number of complete oscillation produced per second or number of crests passing a chosen point per second

Frequency is measured in Hertz.

T= 1/f

If the period, T of the above wave is 0.1 s, (i.e it completes one wave in 0.1s)

It's frequency = 1/T = 1/0.1 = 10Hz

v Velocity: v = frequency x wavelength

Given that the wavelength, λ of the wave is .025m [just as an example]

Then the velocity of this wave in the graph above can be calculated

v = f x λ

= 10 Hz x 0.025

= 0.25 ms^-1

The Wavefront is a line joining all those points on the wave that are in phase (i.e. completed the same amount of oscillation at the same time) All the particles along a crest of a wave are in phase and can be considered as a wavefront