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The law of the levererage

The law of the leverage: an everyday companion

Levers can be found in many different forms 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 the power arm and the load arm

The lever law, which is extremely important in the construction and use 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 power 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 manual force used. 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 power 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 (power 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® achieves a 39-fold increase in hand strength when cutting.  With these pliers, the point of intersection could be set so close to the joint that these side cutters achieve the highest power transmission in the world of side cutters.

 

The wire rope cutter 95 62 160 is equipped with a particularly stable joint. In this way, the distance between the joint and the cutting edge could be kept small, which means that the wire rope cutters have a very high leverage with a length of only 6 1/4" (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