Answer
The speed of a transverse wave is its movement parallel the string, whereas the speed of a piece of the string is a measure of its movement perpendicular to the string.
Work Step by Step
The speed of a transverse wave in a string measures how fast the wave disturbance travels along (parallel to) the string. This is constant, and as shown in equation 11-13, depends on the tension in the string and the linear mass density.
On the other hand, the speed of a tiny piece of the string measures how fast the string element moves perpendicular to the string as the wave passes by. This is not constant: over time, each piece of string moves in simple harmonic motion (shown by equation 11–9).
