Place the ball in the plastic bag, and twist the top so the ball is secure in the bag. Wrap the twisted portion with tape so it stays tight. Use the hole punch or scissors to poke a hole in the part of the bag that’s above the ball. Slip an end of the string through the hole, and tie a knot. This is your pendulum. Hold the loose end of the string still with one hand. With the other hand, raise the ball in an arc so that it’s almost level with the hand holding the string. With the string taut, let the ball go. What do you observe?