The Science of Force and Pressure ,We all know that motion is an integral part of our life. In Class-Vil we have talked about the details of the motion of an object moving along a straight line. We now know that the motion of an object can be uniform or non-uniform in nature. However, we have not yet looked at the cause of motion. When and why does the speed of an object change with time?
We all know that an object at rest does not start moving on its own. Some ‘effort’ is needed to make it move. From our everyday experience, we know that we have to push, or pull, a table, a chair, or an almirah, if we wish to change its position in a room. When we push or pull an object, we are exerting a force. A football, at rest, has to be kicked to send it over a distance. We again say that we are exerting a force on it. We, therefore, say that we exert a force when we push, pull, kick or lift a given object.
In all these situations, some kind of external agency (very often a muscular effort) is involved and its effect can be noticed or felt quite easily. It follows that we need an external force to move a body from its rest position, or to stop a moving body. For example, we can stop a ball rolling down an inclined plane by applying a force against the direction of its motion.
We can thus say that force is a push or pull which comes into play when there is an interaction of one object with another object. For example, when we wish to change the position of a study table in our room, we have to push it. The study table does not move due to our presence alone. There has to be an interaction (push/pull) between us and the study table. The study table begins to move in the direction of the applied force. Thus an interaction of one object with another object can result in a force between the two objects.
The Science of Force and Pressure :- Force
We can now say that: A force is a push or pull upon an object resulting from its interaction with another object Whenever there is an interaction between the two objects, some force acts between them; when the Interaction ceases, the force between them no longer exists. Force exists only as a result of some interaction.
Do You Know?
Force does not always involve effort by living beings like humans or animals. Force can also be due to many natural causes. We may not be able to ‘see’ such forces, but can still feel or observe their effects on objects.
Effects of Force
Change in the state of motion:
A change, in either the speed of an object, or its direction of motion, or both, is described as a change in its state of motion.
We also realise that-
if the applied force acts on a body along its direction of motion, the speed of the body will increase.
if the direction of force, on the body, is opposite to its direction of motion, the speed will decrease. (In both the above two cases, the object is supposed to be moving in a straight line).
if the force acts at an angle to the direction of motion, it can change the speed as well as the direction of motion.
Do You Know?
When a very small body hits a very large body, the forces acting on both the bodies are equal in magnitude but opposite in direction. However, the effect (of force) produced in the small body is very large as compared to the effect of (the equal) force on the larger body.)
Our common experience also tells us that many a time the application of force does not result in a change in the state of rest or motion of the body. For example, we do not observe any motion, when we try to push a heavy stone. A force may not, therefore, always succeed in bringing a change in the state of motion of an object. Sometimes, it only tends to do so.
Change in size/shape of an object:
We know that to make a chapati, we first take the same dough and then roll it between the palms to make it spherical. We can also change the shape of an inflated balloon by gently pressing it between our palms. Some of us might have had a chance to observe the potter at work. A potter makes pots of different sizes and shapes from kneaded clay. In all these situations, the changes in size, or shape, or both take place due to the force applied on them.
We can now say that a force may-
make an object move from rest.
change the speed of a moving object.
change the direction of a moving object.
bring a change in the size, or shape, of an object.
cause two, or more, or all, of these effects.
Do You Know?
An object continues to be in motion, with the same speed and in the same direction, unless acted upon by an unbalanced force. It is a natural tendency of objects to resist any change in their state of rest or motion. This is known as the Law of Inertia
