### String Tension

The *tension* of a vibrating string is the *force* used
to stretch it. It is therefore directed along the axis of the string.
A force must be applied at the endpoint on the right, and a force
is applied at the endpoint on the left. Each point interior to
the string is pulled equally to the left and right,
*i.e.*, the net force on an interior point is
. (A nonzero
force on a massless point would produce an infinite acceleration.)

If the cross-sectional area of the string is , then the tension is given by the stress on the string times .

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Non-Stiff String

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Young's Modulus