Transverse and longitudinal waves

WAVE CHARACTERISTICS

Periodic waves are characterized by a frequency, a wavelength, and by their speed. The wave frequency f is the oscillation frequency of the individual atoms or molecules. The period T = 1/f is the time it takes any particular atom or molecule to go through one complete cycle of its motion. The wavelength is the distance along the direction of propagation between two atoms which oscillate in phase.

In a periodic wave a pulse travels a distance of one wavelength λ in a time equal to one period T. The speed v of the wave can be expressed in terms of these quantities.

v =λ/T =λf

This relationship holds true for any periodic wave.

If the individual atoms and molecules in the medium move with simple harmonic motion, the resulting periodic wave has a sinusoidal form. We call it a harmonic wave or a sinusoidal wave.

If the displacement of the individual atoms or molecules is perpendicular to the direction the wave is traveling, the wave is called a transverse wave.

If the displacement is parallel to the direction of travel the wave is called a longitudinal wave or a compression wave.

Transverse waves can occur only in solids, whereas longitudinal waves can travel in solids, fluids, and gases. Transverse motion requires that each particle drag with it adjacent particles to which it is tightly bound. In a fluid this is impossible, because adjacent particles can easily slide past each other. Longitudinal motion only requires that each particle push on its neighbors, which can easily happen in a fluid or gas. The fact that longitudinal waves originating in an earthquake pass through the center of the earth while transverse waves do not is one of the reasons the earth is believed to have a liquid core.

Дата добавления: 2014-01-05