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Levers

A lever is a simple machine that makes work easier to do. Examples of simple levers include cutting with scissors, or lifting the lid on a tin of paint with a screwdriver. Levers reduce the force needed to perform these tasks.

When someone uses a lever, they exert a force (the effort) around a pivot [pivot: A point around which rotation occurs. to move an object (the load).

A box sits on one end of a see saw which is resting on the ground - 'load'. The pivot is about one third of the way along.  A man stands at the other, raised end, pushing down - 'effort'

A see-saw style lever

Levers rely on the principle of moments [moment: The turning effect of a force. to act as ‘force multipliers’ - they reduce the effort needed to move the load by increasing the distance over which it is acting. This means a relatively small effort force has a much greater effect.

The hammer

A hammer can be used to pull out a nail from a piece of wood.

The man is applying an effort of 12 N on the hammer, the distance between the hand and the wood (pivot) is 0.28 m and the load on the nail Is 50 N. The distance the hammer has to rotate to remove the nail is 0.07 m.

A hammer pulls a nail out of wood

The load force [load force: A force that opposes or resists an effort force. is 50 N and it acts at a perpendicular [perpendicular: At right angles to. distance of 0.07 m. Its moment is 3.5 Nm (50 × 0.07).

The effort force [effort force: The force used to move an object over a distance. acts at a longer perpendicular distance. This is 0.28 m or four times the distance of the load force. As a result, the effort needed is four times less than the load force, or 50 ÷ 4 = 12.5 N.

Note that the moment of the effort is 3.5 (12.5 × 0.28) – the same as the moment of the load.

In this case an effort force of 12.5 N is sufficient to pull against the load force of 50 N, making it relatively easy to pull the nail out.

Other examples

Levers also act as force multipliers in the following examples. Note that the load and effort can both be on the same side of the pivot, as shown in the wheelbarrow example.

Three examples of levers.  1. a man opens a tin of pain with a screwdriver. 2. A pair of scissors cut through string. 3. a man lifts a wheelbarrow filled with soil.

Examples of levers

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