What You Need:
- Empty thread spool
- 2 chairs the same height
- Ribbon just thinner than the spool
- 2 plastic pails with handles
- Pennies or marbles
What You Do:
- Run a piece of sting about 1 foot (30 cm) long through the hole in the spool and tie the ends of the string together.
- Slide the spool and the string onto the broom handle. Rest the handle across the two chairs with the spool hanging between.
- Put one pail on the floor and tie the end of the piece of ribbon to its handle.
- Slide the other end of the ribbon over the spool and tie it to the handle of the other pail, which should dangle in the air.
- Add a few pennies to the hanging pail. What happens to the pail on the ground?
- Return the pail to the ground and add a handful of pennies or marbles. Pull the handle of the hanging pail toward the ground. What happens to the pail filled with weights?
As you added pennies to the hanging pail, it started to lift up the pail on the ground. A single fixed pulley lets you pull in one direction to move a thing in the other direction. This is handy: it means you don't have to climb up a flagpole to raise the flag. Instead, you can stand safely on the ground and pull on the rope as the flag rises to the top!