The big idea: A lever is a rigid beam turning about a fulcrum, with an effort applied at one point and a load resisting at another.
The class is decided by one question only: which of the three sits in the middle?
The same beam three times, with the fulcrum, load and effort moved. The rule becomes visible instead of memorised.
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| Class | In the middle | What follows | Products |
|---|---|---|---|
| First | Fulcrum | Effort and load are on opposite sides, so the movement is reversed. MA can be above or below 1 depending where the fulcrum sits | Scissors, pliers, a crowbar, a see-saw, a claw hammer |
| Second | Load | The effort arm is always longer than the load arm, so MA is always above 1 — it always multiplies force | A wheelbarrow, a nutcracker, a bottle opener, a stapler |
| Third | Effort | The load is always further out, so MA is always below 1 — force is divided and movement multiplied | Tweezers, a fishing rod, a broom, a spade, the human forearm |
F-L-E, in order: 1st: Fulcrum in the middle. 2nd: Load in the middle. 3rd: Effort in the middle.
The first letters run F, L, E — in class order. That single line classifies any lever you are shown.
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MA = effort arm ÷ load arm: Measure each arm from the fulcrum. A crowbar with the effort 600 mm from the fulcrum and the load 40 mm from it has an MA of 15.
The same relationship in moments: effort × effort arm = load × load arm, which is what balances the beam.
Classifying a real product
Find the fulcrum
The point the beam turns about — a hinge, a rivet, an axle, or the edge it rocks on. It is usually the easiest of the three to spot.
Find the load
Where the thing being moved or resisted acts: the nut in the cracker, the barrow's contents, the nail's grip on the timber.
Find the effort
Where the hand is. If the hand grips a long handle, use the point where it actually holds, not the end of the tool.
Name what is in the middle
That is the class. Then measure the two arms from the fulcrum and the mechanical advantage follows.
How this is tested — identifying lever classes and the positions of load, effort and fulcrum. It comes up two ways:
Paper 1 — multiple choice
- Name the class of a lever shown in a drawing.
- Identify which of load, effort and fulcrum is in the middle.
Paper 2 — analysing a product
- Identify the lever class in a named product and explain its effect.
- Explain why a third-class lever was chosen despite its low MA.
The trap: Assuming a third-class lever is a design mistake. It is chosen deliberately: you spend force to buy speed and reach, which is what a fishing rod or a forearm needs.
A kitchen has a wheelbarrow, a pair of tongs and a pair of scissors. Identify the lever class of each, giving the positions of the fulcrum, load and effort.
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