## Kinds of Waves

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

Review **Waves**.

- v = f

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**
F_{T} and the mass per unit length .

- v = (F
_{T}/ )

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 .

- v = (B/ )

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.