Learning objectives By the end of this chapter, you should be able to:
describe what a lever is and how it works explain the turning effect of forces and their calculation in clockwise and anticlockwise moments
state the conditions for equilibrium describe couples and their uses.
Levers
When dealing with equilibrium of forces, it is best to begin with the simplest piece of equipment: the lever. A lever can be a single rigid object that rotates or is pressured against a fixed object (Fig. 6.1).
• The force that is exerted is known as the effort. •
•
The load is the force produced to move something at the other end.
The fulcrum is the point at which a lever turns or is supported.
A lever is a rigid bar, free to rotate about a fixed fulcrum.
FIG. 6.1 The force exerted on a lever moves an object at the other end
effort lever load fulcrum
Turning effect of forces
Forces can cause bodies to rotate as well as move linearly. This is referred to as a turning effect or moment of force. The magnitude of the turning effect de pends on the force and at what dis tance from the axis this force is exerted.
In Fig. 6.2, the axis (or fulcrum) is the point about which the lever turns. It rotates about this axis when a force is applied.
fulcrum or axis
effort = applied force
FIG. 6.2 The fulcrum is the point about which a lever turns
