Using Legos, construct a fulcrum, or center resting spot for your lever. The fulcrum needs to be fairly short and stationary, with a cut-out section where the lever can rest without excessive shifting from side to side. A 12-inch ruler can serve as the lever. Place the ruler in the Lego structure, ensuring that the fulcrum is centered under the ruler.
As the students watch, place a weighted object such as a coin or magnet on the side of the ruler that is currently resting on the floor. Explain that a lever is like a seesaw, and in order to lift the object on one side, an equal or greater amount of force must be applied to the other side. Place an identical object on the other side of the ruler and note what happens. Experiment with various combinations of objects and by placing the objects at different distances from the fulcrum. Point out the differences that occur and explain the reason for the variations in the simplest terms you can.
To explore further differences in weight distribution and the force required to lift an object, shift the ruler slightly so that it is no longer centered on the fulcrum. Explore whether the object is easier or more difficult to lift when the force arm (the side where you apply the force) is longer than the weight arm (the side you are trying to lift) and vice versa. Place the fulcrum at different intervals along the ruler for a variation of outcomes.
Allow the students to construct their own levers using whatever materials they have available: pencils, erasers, Legos, wood blocks and so on. Give them time to experiment with various placements of both the objects on the lever and the lever on the fulcrum. Make a visual assessment of students' understanding of a lever and the factors that affect it.