ABSTRACT
A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force is the newton*, N.
No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are so small. For example, the span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is important for engineers and designers to appreciate the effects of forces on materials, together with their mechanical properties.The three main types of mechanical force that can act on a body are:
(i) tensile (ii) compressive and (iii) shear
Tension is a force that tends to stretch a material, as shown in Figure 3.1. For example,
(i) the rope or cable of a crane carrying a load is in tension
(ii) rubber bands, when stretched, are in tension (iii) when a nut is tightened, a bolt is under tension
A tensile force, i.e. one producing tension, increases the length of the material on which it acts.
