Before understanding Newton’s first law of motion, let us know what is inertia?
Inertia – In daily life we find that force has to be applied to an object to bring it to motion or rest. If a book is placed on the table, the book will remain on the table until an external force is applied, that is, the book is unable to change its state on its own.
If a ball is rolling on a frictionless floor, it will continue to roll with the same velocity in the same direction until it is stopped by an external force. As a result, we find that the ball rolling on the floor stops after covering some distance because the anti-motion frictional force acts between the contact surfaces of the floor and the ball, but if the force of friction is zero, then the ball will move with the same velocity in the same direction. Will keep going. In this way, every object is unable to change its state of rest or movement by itself. This property of an object is called inertia.
It is clear that “An object that is stationary will remain stationary and an object that is moving will continue to move with the same velocity in the same direction unless an external force is applied to it”. The law is called (Newton’s first law of motion).
- Newton has presented the three laws of motion in his famous book ‘Principia’.
- The first law of motion is called the law of inertia.
- Newton’s first law of motion explains the definition of force.
- A force changes the state of motion, rest, shape, or size of an object.
It is clear from Newton’s first law of motion that if an object is at rest, a force must be applied to it to bring it to motion. Similarly, if an object is moving in a straight line with a constant velocity, then a force has to be applied to it to change its velocity. It is also clear that in order to change the direction of motion of an object, a force has to be applied to it.
Newton’s second law of motion
If an object is moving with a uniform velocity, then by the first law of motion the net force on it will be zero. Now if an external force is applied to that object, then its velocity as a result of its momentum will also change. Newton’s second law of motion describes the relationship between the force applied to an object and the rate of change of momentum, which is as follows-
- This law tells how to measure force.
- Force = mass X acceleration.
- Force of S.I. The unit is Newton.
- This law is a fundamental law because from it the first and third laws of motion can be derived.
- the impulse of force = change in momentum
- ∆p = F.∆t
Newton’s third law of motion
According to this law “for every action, there is an equal and opposite reaction.” If a book is placed on a table, the book exerts a downward force on the table due to its weight. According to Newton’s third law of motion, the table also exerts the same upward force on the book. The force exerted by the book on the table is called the action force and the force exerted by the table on the book is called the reaction force.
According to Newton’s third law of motion-
- For every action, there is an equal reaction in the opposite direction.
- This law states that forces are always in the form of pairs.
- Action and reaction forces act on different objects.
Examples of Newton’s third law of motion
- If the string breaks while pulling a bucket full of water from the well, the puller falls backward. The force exerted by the person on the string is action. The opposite reaction force is exerted on the bucket through the tension of the string. When the string is broken the reaction vanishes. Hence the person falls back due to the force of action.
- While firing from the rifle, the rifle wielder gets pushed backward. The reason for this is that when the rifle is fired, due to the explosion of gunpowder, the bullet moves forward with a faster velocity, and the same reaction force on the rifle is applied backward. Therefore, the rifle wielder gets pushed backward.
- When the person on the boat jumps from the boat to the shore, he presses the boat backward with his feet. Nav also exerts a reaction force on the person in the opposite direction due to which the person is able to jump towards the edge.