To make a simple pulley, you need a wire coat hanger, tin snips or wire cutter, an empty wooden thread spool, pliers, string and objects to lift, such as a book, plastic cup or toy car. Cut the bottom portion of the hanger (the base of the triangle) in half. Slide the spool onto the the bottom of the hanger through the cut opening. Push both cut ends through the hole in the spool and bend the ends with the pliers to hold the spool in place and keep the hanger from spreading. Hang the pulley on a closet pole. Tie one end of the string around the object to be lifted. Thread the other end of the string up and over the top of the spool. Pull on the string to lift the object.
For this pulley experiment, you need two desks of the same height, an empty wooden thread spool, 48-inches of ribbon just a bit narrower than the width of the spool, two plastic sand buckets with handles, one foot of string, a rod about four feet long and five cups of sand. Thread the string through the hole in the spool and tie the ends together. Slide the rod through the loop of the string. Position the desks so each end of the rod is on one of the desks with the spool hanging down in between. Tie one end of the ribbon around the handle of a sand bucket. Place it on the floor between the two desks. Pull the ribbon over the spool. Tie the remaining end of the ribbon to the second sand bucket so the bucket hangs in the air. Put a cup of sand into the hanging sand bucket. Record your results. Empty the hanging sand bucket, and put five cups of sand in the sand bucket on the floor. Pull down on the handle of the empty hanging sand bucket. Note how the pulley makes your work easier.
Try another variation of the simple pulley using 12 inches of string, an empty wooden thread spool, a large paper clip, 36 inches of ribbon just a bit narrower than the spool, masking tape and a toy car weighing about one pound. Thread the string through the hole in the spool and tie the ends together. Open one end of the paper clip to make a hook. Hang the toy car from the hook. Attach the other end of the paper clip to the string. Tape one end of the ribbon to the edge of a table. Thread the ribbon under the spool and pull up and down on the ribbon.
To combine two simple machines, the pulley and the belt, you need an old-fashioned roller skate with four wheels and a rubber band at least 1/4-inch wide. On one side of the skate, wrap the rubber band around one wheel and then the other wheel. Turn one wheel and the other wheel will also turn. Remove the rubber band from one wheel, and give it half of a twist. Put it back around the wheel. Turn one wheel and the other turns in the opposite direction.