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The law of the lever


The law of the lever: an everyday companion

Levers, in all their different forms, can be found in everyday life. They serve to transform the applied force.


A lever is often used to convert small forces – e.g. your own muscle strength into larger forces.

An unknown artist shows how Archimedes uses a lever on the globe. The Greek was the first to formulate the law of the lever and thus the theoretical basis for the later development of mechanics. (Source: pa)


The lever: from effort arm and load arm

The extremely important law of the lever in the construction and application of pliers goes back to the Greek scholar Archimedes. In the 3rd century BC he formulated the previously known principle of the lever. In doing so, he set up the formula "Effort times effort arm equals load times load arm".


In practice, this means that a force applied to a long lever - the effort arm - is able to move a multiple load on the correspondingly shorter load arm. Archimedes succinctly illustrated the law of the lever with the sentence attributed to him: "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."



A pair of pliers: the connection of two levers with a common pivot point


An important function of pliers is to increase the applied effort. With the right design of the pliers handles, the joint and the gripping jaws or cutting edges, engineers can construct such a high transmission ratio that the user's manual force can be multiplied several times. The reach of the human hand limits the opening width and thus the possible length of the effort arm. That is why the construction of the joint is of particular importance.


Because the smaller the distance between the intersection and the joint (load arm) and the longer the lever (effort arm), the greater the cutting force or the higher the lever ratio. If the handles are shorter, the leverage is smaller and less force is available for cutting.


Thanks to its special joint construction, the KNIPEX TwinForce® multiplies the applied hand force times 39. The intersection could be set so close to the joint that this diagonal cutter achieves the highest force transmission in the world of side cutters.


The wire rope cutter 95 62 160 is equipped with a particularly stable joint. It also keeps the distance between the joint and the cutting edge small, which results in a very high leverage at a tool length of only 160 mm.

With a hand force of 500 N, the KNIPEX TwinForce® provides a cutting force of up to 19,500 N, i.e. 39 times the applied hand force.

FS = cutting force, FH = hand force, l1 = effort arm, l2 = load arm