Simple machines can make our work easier. The demonstration below shows how a pulley can save time and effort in lifting.
pulley (an inexpensive one will do)
string of a size appropriate to your pulley
chalkboard with hooks at top
You are going to demonstrate how a pulley works as well as how it can make work easier. Before showing the pulley to the class, describe a situation in which it would be needed. For example, you and your friends have a tree house and need to get food up to it for a tree-top picnic. The trouble is you need both hands for safely climbing the ladder. How do you get the food into the tree house? (Backpacks would limit what you could transport by weight; transporting by backpack might also set you off balance. Throwing the food up to the tree house would be messy.)
Make an illustration of this situation on the board, drawing the tree, tree house ladder, and friends. Make the tree as high as the chalkboard, with one limb running parallel to the hooks at the top. (This is where the pulley will be attached.)
Did the class find a solution? Offer the pulley as a tool to help. Hook the pulley onto the top of the chalkboard (tree limb) and rig the string to it. Punch a hole near the rim of the paper cup and tie one end of the string to it. Demonstrate how the pulley could transport supplies up and down.
Have the students seen pulleys at work before? Where?
If desired, have them illustrate uses for the pulley -- real and imagined. Have them share their illustrations with the class.