Simple harmonic motion

1. Sep 12, 2006

Bim

When observing the acceleration graph of simple harmonic motion we can see that the acceleration is just the opposite of the elongation. Yet we know that the pendulum velocity is increasing when approaching the equilibrium state. Which means that the motion is accelerated altough the sign of the acceleration is negative. How to understand this contradiction?

2. Sep 12, 2006

Staff: Mentor

The restoring force, and the resulting acceleration, always points towards the equilibrium point.
That's what acceleration does!
The acceleration is always toward the equilibrium point. Thus when the object moves towards equilibrium, its speed increases: both its acceleration and velocity will have the same sign. (Both negative on one side of equilibrium, both positive on the other.)

Realize that something with a negative velocity and a negative acceleration will speed up.