Simple harmonic motion is sinusoidal – it can be expressed in terms of
or
functions or a sum of
and
functions.
or
all imply simple harmonic motion.
If
then we can find the velocity
and the acceleration
by differentiation:
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This is illustrated in the diagram below.

Notice that
and
have opposite signs, and
is
larger in magnitude.
The displacement leads the velocity by
of a cycle and the velocity leads the acceleration by
of a cycle.