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Lay a pencil on its side and use clear tape to firmly fasten it to a tabletop. Leave about 1⁄2 inch (1.3 cm) of the pencil hanging over the edge. The pencil will anchor your pendulum and keep it from falling down, so be sure to use enough tape to secure it and keep it from moving around. Test the pencil by flicking it with your finger. It should stay stuck to the tabletop. Take a length of string 2–3 feet (0.61–0.91 m) long and curl one end to form a loop. The loop needs to fit around the pencil, but not too tight or it won’t swing properly. Tie a knot with the loop to keep it from coming undone. Slide the loop onto the pencil and slide it off to make sure it’s not too tight. Take a 2 in (5.1 cm) length of metal wire and curl one end of it into a “J” shape to form your hook. The hook will hold the weight that swings the pendulum so shape your hook so it’s easy to attach and remove nuts onto it to alter the weight of the pendulum. You can use pliers to curl the metal wire. Use a standard metallic nut as the weight for your pendulum. The hole in the center makes a nut ideal for sliding onto the hook, and you can easily add or remove nuts to experiment with different weights. Slide the nut onto the hook so that it’s not able to fall or slide off when the pendulum swings. Do not close the hook around the nut. You can use the paper to mark where you release the pendulum each time so you can see the way the pendulum behaves and swings based on where you release it. Tape the paper so that it is a backdrop behind the hook with the nut on it. Any color paper is fine, as long as you can see the pencil markings.

Summary:
Tape a pencil horizontally to the top of a table. Tie a loop about 1 inch (2.5 cm) in diameter at one end of a string. Make a small 1⁄2 inch (1.3 cm) hook with a metal wire. Slide a 1⁄4 inch (0.64 cm) nut onto the end of the hook. Tape a piece of paper on a wall or table behind the hook.