We have observed that, if we put an object in motion it comes in state of rest. But if we put any object in state of rest it remains in that state. For example, if we throw a ball upward or roll it on the ground, it will ultimately come in the state of rest, but if the ball is already in the state of rest, it does not start moving on its own. In our previous episode we discussed that, every object tends to stay in its state until and external force compelled to change the state. So how this ball is changing its state of motion on its own. A simple answer is, there are always some kind of invisible forces in action. For example, when the ball is thrown in the sky, gravitational force is in action and when the ball is rolling on the ground, frictional force is in action. Thus, the ball is coming back to its rest state. We will discuss these two forces in our upcoming episodes.
For a better understanding, let us suppose an object is in the space and no gravitational force, electrostatic force or frictional force is in action. Now if the object is left undisturbed, it will remain undisturbed for always and if the object is provided some initial speed, it will keep moving in straight line with constant speed for always without acceleration. In other words, we can say that every object offers a resistance to change its state of motion. If it is in rest, it tends to stay in rest and if it is moving it tends to remain in motion. In terms of physics, this property of object is known as inertia.
From Aristotle to Galileo, this was a serious topic of discussion for centuries. Finally in 1687 Newton proposed his laws of motion in his famous book “principia”. In which he proposed three laws of motion. First law of Motion is known as law of inertia. This law state that, everybody perseveres in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed thereon.
There are loads of daily life examples explained based on this law. Like traveling in bus and car, carrom coins, cleaning clothes by shaking it in the air etc.
