Kinds of Waves

READ: Sections 12.7, 8; EXAMPLES: 10, 12; PROBLEMS: 67, 70, 83, 85

Review Waves.

In waves on a stretched string, the parts of the string move in a direction perpendicular to the motion of the wave itself (for example up and down, while the wave moves to the right). This is called a transverse wave.

The velocity of a transverse wave depends on the tension force FT and the mass per unit length .

Note that this is not the same as the velocity of a particle of the string. This particle moves in SHM, and its velocity varies between +A and -A, where = 2/T and A is the amplitude of the wave.

Sound waves in a fluid such as water or air are examples of compression or longitudinal waves. In these waves the particles (molecules) of water or air move back and forth along the direction of the wave, causing compression and rarefaction.

The velocity of a compression wave depends on the Bulk Modulus B of the fluid and the mass per unit volume .

Note that in both formulas for wave velocity, the numerator represents a quantity which tells how "stiff" the material is, and the denominator represents a quantity which tells how massive it is.

Click here to see some animations which demonstrate transverse and longitudinal waves.