Wave Properties Unit 8.4

Wave Motion A pebble dropped into a pond creates ripple waves which are due to a disturbance at some point in the water.

Wave Motion This disturbance causes water on the surface near that point to move. In this way, the waves travel outward in a circular pattern away from the original disturbance.

Wave Motion In this example, the water in the pond is the medium through which the disturbance travels. Particles in the medium vibrate up and down as waves pass.

Wave Motion Note that the medium does not actually travel with the waves. After the waves have passed, the water returns to its original position.

Wave Motion Waves of almost every kind require a material medium in which to travel. Sound waves cannot travel through outer space because space is nearly a vacuum. In order for sound waves to travel, they must have a medium such as air or water.

Wave Motion Waves that require a material medium are called mechanical waves. Not all wave propagation requires a medium. Electromagnetic waves can travel through a vacuum.

Wave Types One of the simplest ways to demonstrate wave motion is to flip one end of a taut rope whose opposite end is fixed. The flip of your wrist creates a pulse that travels to the fixed end with a definite speed.

Wave Types A wave that consists of a single traveling pulse is called a pulse wave.

Wave Types Now imagine that you continue to generate pulses at one end of the rope. These multiple pulses form what is called a periodic wave.

Wave Types A wave in which the particles of the disturbed medium move perpendicularly to the wave motion, is called a transverse wave.

Wave Types A picture of a wave, like the one like below, is sometimes called a waveform.

Wave Types A wave is measured in terms of both its displacement from equilibrium and the distance between neighboring displacements.

Wave Types The highest point above the equilibrium position is called the wave crest. The lowest point below the equilibrium position is the trough of the wave. The distance between adjacent crests or troughs is always the same.

Wave Types A waveform can represent either the displacements of each point of the wave at a single moment in time or the displacements of a single particle as time passes.

Wave Types A particle in the wave is displaced first in one direction, then in the other direction, finally returning to its original equilibrium position ready to repeat the cycle. Thus, a wave can be thought of as a cyclical motion.

Wave Types The distance the wave travels during one cycle is called the wavelength. This is represented by the Greek letter lambda λ

Wave Types You can create another type of wave with a spring. As this wave travels to the right, the coils of the spring are tighter in some regions and looser in others.

Wave Types The displacement of the coils is parallel to the direction of wave motion, so this wave is a longitudinal wave.

Wave Types Frequency describes the number of crests or troughs that pass a given point of a unit of time and is measured in Hertz (Hz) or 1/s. The period of a wave is the amount of time required for one complete vibration of the particles of the medium.

Wave Types The relationship between period and frequency is as follows: period  frequency (inversely proportional)

Wave Types To measure the speed of a wave, we use the following formula: v = f *  (m/s) The speed of a mechanical wave is constant for any given medium.

Wave Types Although the frequencies and wavelengths of the sounds produced by each instrument maybe different, the product of the two are the same.