Before the lesson, assemble the wheel and axle unit, and clip a piece of skewer to make a handle.
Attach the binder clips to the box, each with the inner handle flipped up. Thread the wooden dowel through the handles - the wheel should spin easily.
Wrap the play dough around the dowel, to give it weight.
To turn the wheel, insert the handle into the outer straw in the wheel.
Then try with the handle in the inner straw.
Which is easiest?
The handle in the outer position should make it much easier to turn the wheel - not much force is needed.
The handle in the inner position requires more force, and might be quite hard to turn the wheel at all.
The difference in force is balanced by the distance you move your hand: the outer position it moves further around the outside edge of the wheel, whereas at the inner position it does not move so far.
Hence, a wheel makes work easier, by decreasing the force required, while increasing the distance moved.
Real life applications:
Door handle - we turn the outside of the handle (wheel) with little force (but over a greater distance) which turns the shaft (axle) of the handle over a smaller distance but with a greater force.
Any device where we turn a wheel using the outer edge or a long handle, which makes the inner shaft turn.
Water wheel - water hits the outside of the wheel and is able to turn the wheel, generating a larger turning force at the axle which can wind a rope or turn a stone.