Lever Effect
The water wheel acts as a lever, one of the five simple machines. Take two paper plates and glue them back to back. Take 10 Styrofoam cups and cut off the tops. Discard the tops and hot glue the bottoms around the Styrofoam plate wheel with the tops facing up. Take a wooden dowel. Find the center of the wheel and mark it. Cut a hole in the center about the same size as a wooden dowel and slide the dowel through, gluing it in place on both sides. Take a small nail and nail it into the dowel close to the plate. Then, tie a long piece of string to it.
The Lever Effect in Action
Do the next part outside to avoid water splashing. Take two straight-back chairs and set them back to back and a couple of feet apart. Place the dowel rod across the backs of the chairs. Attach a small weight, such as a stapler or small bucket, to the other end of the string. Now pour water into a cup close to the top of the wheel, but not directly on the top. The wheel will start to turn. Try different water sources, like a squirt gun or water hose. Observe whether or not the water source makes a different in the amount of weight the wheel can pick up.
How It Works
The water wheel operates on the principle of the lever, which means that the amount of weight lifted depends on the size of the wheel, no matter the water source. When you have a bigger wheel, the bigger wheel multiplies the force of the water over a greater distance. Force times distance equals greater force.
Small Scale Water Wheel
Construct a wheel on a smaller scale to further demonstrate how water wheels work. Tape small rectangles of cardboard length-wise as blades on a cork. Bend another piece of cardboard into a 'U̶1; shape to hold the waterwheel. Stick a long pin through one end of the ̶0;U,̶1; through the waterwheel and into the other end of the U. Tape a piece of string to the axle and set the wheel on a chair so the string can hang freely. Attach the same weighted item to the other end of the string. Use the same water sources to try to raise the weighted item. You'll find that the smaller water wheel either won't be able to raise the item, or won't be able to raise it as well as the larger wheel.