Page 95 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Lever: A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever
is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the
lever is divided into three types. It is one of the six simple machine identified by Renaissance scientists. A lever
amplifies an input force to provide a greater output force, which is said to provide leverage, which is mechanical
advantage gained in the system, equal to the ratio of the output force to the input force. As such, the lever is a
mechanical advantage device, trading off force against movement.

• Class I - Fulcrum is located between the effort and the resistance: The effort is applied on one side of the
fulcrum and the resistance (or load) on the other side. For example, a seesaw, a crowbar, a pair of scissors,
a balance scale, or a claw hammer (pulling a nail). With the fulcrum in the middle, the lever’s mechanical
advantage may be greater than, less than, or even equal to 1.
• Class II - Resistance (or load) is located between the effort and the fulcrum: The effort is applied on one side of
the resistance and the fulcrum is located on the other side, e.g. a wheelbarrow, a nutcracker, a bottle opener,
or the brake pedal of a car. Since the load arm is smaller than the effort arm, the lever’s mechanical advantage
is always greater than 1. It is also called a force multiplier lever.
• Class III - Effort is located between the resistance and the fulcrum: The resistance (or load) is applied on one
side of the effort and the fulcrum is located on the other side, e.g. a pair of tweezers, a hammer, a pair of tongs,
a fishing rod, or the mandible of a human skull. Since the effort arm is smaller than the load arm, the lever’s
mechanical advantage is always less than 1. It is also called a speed multiplier lever.

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CITS : WCS - Mechanical - Exercise 8