Move a load by changing the effort arm, the load arm and the position of the pivot.
A lever turns about a fulcrum. The effort force is the input; the load force is the resistance being moved or balanced. An arm is a perpendicular distance from the pivot to the line of action of a force.
A larger force has a larger turning effect at the same arm. A longer perpendicular arm has a larger effect at the same force. For a balanced ideal lever, effort force × effort arm equals load force × load arm.
In a first-class lever, the fulcrum is between effort and load. In a second-class lever, the load is between fulcrum and effort. In a third-class lever, the effort is between fulcrum and load. Third-class levers often provide greater output movement or speed rather than a larger output force.
Simple calculations may neglect lever weight, pivot friction and bending. A real tool must withstand the load. Use small, teacher-approved loads for classroom investigations; do not use people or hands as supports.
Open Balance Lab. Put unequal masses on opposite sides and move them until the board balances. Use the rulers to compare mass × distance. Remove the supports to test your prediction.
The balance board is an idealized lever. Use distance from the pivot rather than the gap between objects.
Science North · Mechanism in action
Identify all three lever classes, then compare the effort and load arms. Pause before each demonstration to predict what will change.
A 20 kg mass sits 1 m from a pivot. Where could a 10 kg mass balance it?
At 2 m on the other side, assuming a weightless balanced board and the same gravitational field: 20 × 1 = 10 × 2.
Keep a pair of masses fixed. Find two different balanced arrangements and explain the pattern.
Apply it to the design challenge →Read further: OpenStax · Simple Machines →
