lever

lever

1. a rigid bar pivoted about a fulcrum, used to transfer a force to a load and usually to provide a mechanical advantage

2. any of a number of mechanical devices employing this principle

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

lever

[′lev·ər, lē·vər]

(engineering)

A rigid bar, pivoted about a fixed point (fulcrum), used to multiply force or motion; used for raising, prying, or dislodging an object.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Lever

 

a simple machine consisting of a rigid element that pivots about a fixed support (fulcrum) and enables a smaller force to balance a larger one. The operating principle behind any type of lever can be expressed by the equality Ph₁ = Qh₂, where P and Q are the applied forces, and h₁ and h₂ are the lever arms, that is the perpendicular distances from the fulcrum to the line of action of each force.

Figure 1. Levers: (a) first-class, (b) second-class

If the fulcrum is positioned between the points where the forces are applied, the machine is called a first-class lever (Figure 1, a). If both forces are applied on the same side of the fulcrum, the machine is a second-class lever (Figure 1, b). With first-class levers, the forces must take the same general direction; with second-class levers, the forces assume different directions. Archimedes developed the theory of equilibrium for levers balanced by weights, and the general condition for lever equilibrium was worked out by P. Varignon in 1687. Levers are often used as simple lifting devices.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.