Introduction to SAT II Physics

A string is tied to a pole at one end and 100 g mass at the other, and wound over a pulley.

The string’s mass is 100 g, and it is 2.5 m long. If the string is plucked, at what speed do the

waves travel along the string? How could you make the waves travel faster? Assume the

acceleration due to gravity is 10 m/s^2.

Since the formula for the speed of a wave on a string is expressed in terms of the mass
density of the string, we’ll need to calculate the mass density before we can calculate the
wave speed.

The tension in the string is the force of gravity pulling down on the weight,

The equation for calculating the speed of a wave on

a string is:

This equation suggests two ways to increase the speed of the waves: increase the tension
by hanging a heavier mass from the end of the string, or replace the string with one that is
less dense.

Longitudinal Waves: Sound

While waves on a string or in water are transverse, sound waves are longitudinal. The
term longitudinal means that the medium transmitting the waves—air, in the case of
sound waves—oscillates back and forth, parallel to the direction in which the wave is
moving. This back-and-forth motion stands in contrast to the behavior of transverse
waves, which oscillate up and down, perpendicular to the direction in which the wave is
moving.
Imagine a slinky. If you hold one end of the slinky in each of your outstretched arms and
then jerk one arm slightly toward the other, you will send a pulse across the slinky toward
the other arm. This pulse is transmitted by each coil of the slinky oscillating back and
forth parallel to the direction of the pulse.