**PURPOSE: **To demonstrate standing waves in a stretched wire and to demonstrate Mersenne's laws.

**DESCRIPTION: **This device can be used to demonstrate Mersenne's three laws for stretched strings.Keeping two of the three variables constant:

(1) the fundamental frequency is inversely proportional to the length of the string. A stop is inserted under a point on the string, dividing the string into two segments.

(2) the fundamental frequency is directly proportional to the square root of the tension. Note the frequency of the thinner string with five kilograms of weight. Quadrupling the weight doubles the frequency, raising it one octave.

(3) the fundamental frequency is inversely proportional to the square root of the mass per unit length. The thicker string is about twice the diameter or four times the mass per unit length of the thinner string. With the same weight the pitch of the thicker string is about one octave lower. The thicker string must have about four times the tension (hanging mass) of the thinner string to make their fundamental frequencies the same.

**SUGGESTIONS: **

**REFERENCES: ** (PIRA 3D20.10)

**EQUIPMENT: **Sonometer with 25 kG of weights and stops.

**SETUP TIME: **None.