Effects of Force
1. Force and Change in Motion Motion is important to our lives and it affects so many things that we do. Motion is the change in position of an object. We have already seen that the force can produce motion in a body. Force can also stop a moving body. Another effect of force is that it can change the motion of a body by moving it faster or slower. Let us demonstrate it by an example. Suppose your friend is riding his bicycle. If you gently pull the moving bicycle from behind, it slows down (Figure 7.4a). Again, if you give it a push, it moves faster (Figure 7.4b). This means that if a force is applied in an opposite direction of motion of a body, the body will slow down or stop. But if force is applied in the direction of motion, the body will move faster.
Figure 7.4
Greater the force, greater will be the distance covered by the object. 2. Force and Change in Direction of Moving Object Force not only makes the objects move slow or fast but it can also change the direction of the moving objects. For Example, when a batsman hits the ball with bat, his force not only moves the ball faster but changes its direction as well (Figure 7.5). Similarly, a football player changes the direction of motion of the ball by kicking it with his foot (Figure 7.6).
Figure 7.5 Figure 7.6
3. Force and Change in Shape of the Objects What happens when we apply force to a rubber band? It stretches out. But when we remove the force, the rubber band shrinks back to its original shape. A force can stretch, compress, squeeze and cause change in the shape of the objects. The change in the shape of the objects, when a force is applied may be temporary or permanent. Let us understand how force changes the shape of objects temporarily.
From the above activities we can observe: Some objects return to their original shape after the removal of force. These objects are called Elastic objects.
Shape of some objects is changed permanently when force is applied on them. For example, the molding of clay is a permanent change in shape by the force (Figure 7.7).
From this activity we can observe: Some objects do not return to their original shape after the removal of force. These object are called inelastic objects.