Teaching Physics with the Physics Suite Edward F. Redish

Graphing a pulse on a string

Consider the motion of a pulse on a long taut string. We will choose our coordinate system so that when the string is at rest, the string lies along the x axis of the coordinate system. We will take the positive direction of the x axis to be to the right on this page and the positive direction of the y axis to be up. Ignore gravity. A pulse is started on the string moving to the right. At a time t0 a photograph of the string would look like figure A below. A point on the string to the right of the pulse is marked by a spot of paint.

For each of the items below, identify which figure above would look most like the graph of the indicated quantity. (Take the positive axis as up.) If none of the figures look like you expect the graph to look, write N.
1. The graph of the y displacement of the spot of paint as a function of time.

2. The graph of the x velocity of the spot of paint as a function of time.

3. The graph of the y velocity of the spot of paint as a function of time.

4. The graph of the y component of the force on the piece of string marked by the paint as a function of time.

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