"I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."
~ Sir Isaac Newton
Sir Isaac Newton (1642-1726): A Mathematician, Astronomer and Physicist was born at Wollsthrope in England. He worked in many area of Mathematics and Physics.
He developed the theories of gravitation in 1666, when he was only 23 years old. After some year later, he presented his three laws of motion in the book: "Principa Mathematica Philosophiae Naturalis" in 1687.
(If the net force is zero: Object at rest, stay at rest. And Object in motion, continue to move).
This means that, there is a natural tendency of objects to keep on doing what they're doing. There is no change in the state (rest or motion) without an external force acting. That is, a force is an agent that produces a change in state of a body.
#2. Newton's $2^{nd}$ Law:
"The rate of change of momentum of a body with respect to time is directly proportional to the net external force acting on the body."
However, Newton's second law gives us an exact relationship between force, mass and acceleration. Mathematically,
$F_{net} = ma$
i.e.net force on object = mass of object * acceleration
If we exert the same force on two objects of different mass, we'll get different acceleration (change in motion).The heavier objects require more force to move than the lighter objects.
Note: In equation, $F = ma$; if net force acting on a mass is zero then, $a=0$.
This means that, if the net force acting on a body is zero, it moves with constant velocity or it will be rest. Which is the statement of the Newton's $1^{st}$ law.
#3. Newton's $3^{rd}$ Law:
"To every action there is always an equal and opposite reaction."
This means that, for every action there is equal and opposite reaction. It dose not matter which force we call action and which we call reaction.
All forces always occur in pair. For example: During the simplest act of walking, we push against the road surface with our shoes and road pushes back with an equal force but in opposite direction. It is the force the road exerts on us that causes us to move forward.
Similarly, at the swimming time a swimmer moves through the water only because he pushes water backward and the water pushes the swimmer forwards.
Again, Let's understand how a rocket works. The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.
"A body remains in the state of rest or in the state of uniform velocity if no net force is acting on it."
