Steering Wheel -
It is made up of a Wheel and a Pulley. A pulley is a simple machine consisting of a wheel through which is run a chain or rope that can be attached to a heavy object that can be lifted or moved. The direction in which force is exerted to lift a heavy object is changed when a pulley is used. A wheel is used to move heavy objects or a wide variety of tools, toys and household objects, serving many different purposes with great efficiency. The steering wheel is made up of both of them.
Teeter Totter -
If the fulcrum is in the center, and two kids of equal weight are on the ends, then they won't move up or down unless they push with their legs. They are in balance and there is no mechanical advantage. If one kid weighs more, but the fulcrum hasn't moved, still centered, then the heavy kid will stay down until he pushes with his legs. There is still no mechanical advantage. Now, pick up the board and move it so that the fulcrum is off center toward the lighter kid. If you adjust it right, the extra length of the board on the light-kid's side will give him mechanical advantage or "leverage" to help him balance against the heavier kid's weight.