Drag the pendulum to an angle (with respect to the vertical) of 30∘ , and then release it. Select to show the acceleration vector. With the pendulum swinging back and forth, at which locations is the acceleration equal to zero? The acceleration is zero when the angle is 0∘ . The acceleration is zero when the angle is either +30∘ or −30∘ . The acceleration is never equal to zero as it swings back and forth.