Start and Stop the animation using the button.
The acceleration of a pendulum is of course a maximum at the two extremes, when the velocity is zero - that's the hallmark of simple harmonic motion. At the bottom of the travel, the velocity is a maximum, however, the pendulum bob is still moving in a curved way, so there must be an acceleration towards the center of the circle. This sim shows the two vectors and the continuous dance back and forth during the oscillations.
Link to stand-alone sim: Here is a link to view the sim on its own, with no distractions.