Procedure: Introduce this topic by asking students about how they might place a piece of cardboard so a pair of scissors could cut it easily. Then ask each group to try their idea on a small piece of heavy cardboard using the How to use a Pair of Scissors Worksheet. For each position of the cardboard, have them identify the effort, fulcrum, load, effort arm and load arm; and explain how the two arms change as the cardboard is moved towards the center.

When a pair of scissors doesn’t cut a piece of cardboard very well, what do you do? Most people would suggest moving the cardboard from A to B puttting it closer to the pivot.

Why does this work? Some would say that the blades are sharper nearer the pivot, but that might not always be true. A more reliable explanation has to do with levers. Let’s look again at the two configurations, using the language of levers. Here are some new terms:

Effort arm = Distance from fulcrum to input, or effort point

Load arm = Distance from fulcrum to output, or load point

Mechanical advantage = Ratio of	effort arm
	load arm

Later, we’ll see why this ratio is called “mechanical advantage.” For now, let’s think about what happens when we move the cardboard from A to B.