lever

Types of lever. Practical applications of the first-order lever include the crowbar, seesaw, and scissors. The wheelbarrow is a second-order lever; tweezers or tongs are third-order levers.

Simple machine consisting of a rigid rod pivoted at a fixed point called the fulcrum, used for shifting or raising a heavy load or applying force. Levers are classified into orders according to where the effort is applied, and the load-moving force developed, in relation to the position of the fulcrum.

A see-saw is an example of a simple lever. An effort force at one end is used to lift a load force at the opposite end, with a turning motion about the pivot. A see-saw can also be used to demonstrate the balancing of the moments of a force. The formula used to work out the force needed and the distance of the force from the pivot to balance the see-saw is: effort force × distance from pivot = load force × distance from pivot.

A first-order lever has the load and the effort on opposite sides of the fulcrum – for example, a see-saw or pair of scissors. A second-order lever has the load and the effort on the same side of the fulcrum, with the load nearer the fulcrum – for example, nutcrackers or a wheelbarrow. A third-order lever has the effort nearer the fulcrum than the load, with both on the same side of it – for example, a pair of tweezers or tongs. The mechanical advantage of a lever is the ratio of load to effort, equal to the perpendicular distance of the effort's line of action from the fulcrum divided by the distance to the load's line of action. Thus tweezers, for instance, have a mechanical advantage of less than one.