The free end of a simple pendulum is attached to the ceiling of a box. The box is taken to a height and the pendulum is oscillated. When the bob is at its lowest point, the box is released to fall freely. As seen from the box during this period, the bob will

when the box is released the pendulum inside it will feel weightlessness and therefore there is no gravitational effect on it.

But the bob is released at the lowest point in which it has the maximum speed; therefore it does feel the effect of centrifugal force. Which give rise to tension in the wire and the length of the pendulum remain constant.

So it moves in a circular path.