Make an inclined plane by placing a sturdy piece of plywood so that one end connects to a higher surface and another edge connects a lower surface, such as the edge of an auditorium stage. Move a box from the higher surface to the lower surface both with and without the inclined plane to demonstrate the purpose of this simple machine.
Draw a circle on another plywood board using your carpenter's compass. Draw a straight line through the center. Mark the exact center of the compass by measuring the diameter, dividing that number by two, and marking that spot inside your circle. Duplicate this process to produce another circle with its own center mark.
Drill a hole centered on the center mark of your circle. Use a bit wide enough so that your dowel rod can fit through. Repeat in your other circle.
Cut the circles out of the plywood sheet with a saw. You may use a saber saw to go faster, but make sure to take proper safety precautions. If your wheels are small enough, you might even use a drill press with a circle bit.
Slide your dowel rod into the holes in your circles, leaving one circle about 2 inches from each end of the dowel rod. Demonstrate how a small application of force on the dowel rod causes the circles to cover a greater distance now that they function as the simple machine called the wheel.
Connect saddle clamps to the ends of the dowel rod that reach out beyond the wheels. These will just slide into place. Screw the other end of each saddle clamp to the plywood sheet you used as an inclined plane.
Demonstrate the compound machine called the wheelbarrow by flipping the plywood sheet over so that the wheels touch the ground. Use the rudimentary wheelbarrow to move your box from one end of the room to the other by placing the box on the plywood and then lifting at the end without wheels. Show how it is easier to move the box with the use of this compound machine.