Laboratory work. The equilibrium condition of a lever
You need: a ruler balanced on a support (a lever), a set of equal weights (for example 50 g masses), thread and a dynamometer. Place the ruler on the support and make it horizontal. Hang several weights on the left arm and hang weights on the right arm so that the ruler again stays balanced horizontally. Measure each arm — from the support to the point where the weights hang — with a ruler, and find the weights of the loads from F = m · g. Then calculate F₁ · l₁ and F₂ · l₂ and compare: they are about equal, and any difference is measurement error (friction, mass of the ruler, difficulty in finding exact balance). Repeat with 3–4 different arms and loads and write the results in a table. Conclusion: the smaller the force, the longer its arm must be.
Laboratory work (in pairs): balance the lever and run the experiment with 3 different loads and arms, filling in the table: “F₁, l₁, F₁·l₁, F₂, l₂, F₂·l₂”. Safety: do not drop weights on your feet, use a plastic rather than a glass support, and keep fingers out from between support and ruler.