Learning objectives
- Identify fulcrum, load and effort.
- Classify levers by the middle point.
- Use arm lengths to calculate ideal effort.
- Explain force–distance trade-offs and losses.
Key equations
Ideal: Fe × a = FL × b. IMA = a/b. Actual MA = η × IMA. FL = mg. Effort Fe = FL/MA.
For vertical forces at bar angle θ, the perpendicular moment arms are a cos θ and b cos θ. Their common cosine cancels. Input work uses vertical displacement, not the curved arc distance of an endpoint.
Model assumptions
A rigid, massless lever moves slowly through a small angle. Inertia is neglected; a supplied operator provides the calculated effort. Efficiency represents lumped friction and deformation losses. The ideal moment equation does not include those losses.
The wheelbarrow tips about a stationary axle. The fishing rod is a rigid teaching model and does not include bending. Each illustration uses its own drawing scale. Arm edits preserve the selected class by adjusting the other arm when needed.