NEWTONS LAWS OF
1. Newtons first law of motion states that, “Every object will remain at rest or in uniform
motion in a straight line unless compelled to change its state by the action of an external
2. Newtons second law of motion states that, “Force is equal to the rate of change of
3. Newtons third law of motion states that, “Every action has an equal and opposite
WHY LAWS OF MOTION?
We use the concepts of laws of motion to explain the way macroscopic objects interact and
influence the motion of each other. It is a good approximation for replicating most circumstances in our
physical world. Newtons Laws of Motion is base on three laws given by Newton. It is used to describe
the motion of the Centre of Mass of a object. (Along with Rotational Mechanics it can describe a lot of
motions, both translatory and rotational)
1ST LAW OF MOTION
An object which is initially in rest or uniform motion will continue to do so unless an external
unbalanced force is applied. Say a boat is floating stationary in a sea. The wind catches the sail and
applies a force on the boat. This causes the boat to start moving.
The boat is stationed The boat starts
The Sun pulls the Earth with its
gravitational force, thus changing the
direction of Earth so, Earth does not fly
o f f i n t o s p a c e
Α moving ball hits a wall, which applies a force
o n t h e b a l l , s t o p p i n g i t
The faster the wind blows, the faster the sailboat will start sail. This implies that the rate at which
velocity increases is proportional to the magnitude of force applied. This rate of change of velocity is
termed as acceleration.
Thus, acceleration ∝ force
ACCELERATION AND MASS
On the other hand, in the same wind, a lighter sailboat will start to move faster than a heavy sailboat.
This implies that the same force can accelerate a lighter body much more than it can accelerate a
heavier body. Acceleration is inversely proportional to mass of the body
Thus, acceleration ∝ 1/mass
3RD LAW OF MOTION:
Every action has an equal and opposite reaction. Take a wheel for example. The wheel rotates and
apples a force on the ground. Due to this, the ground also applies an equal force to the wheel, which
pushes it forward. Its because of this that when an object strikes another, both start moving in
opposite directions regardless if it was stationary or moving.