NEWTON'S LAW OF MOTION

Newton’s Law of Motion

Sir Isaac Newton was an English mathematician, astronomer and physicist who gave three laws which proved to be fundamental laws for describing the motion of a body. These are generally known as Newton’s laws of motion. We will discuss each law of motion one by one in detail.

Newton’s First Law of Motion:

Newton’s first law of motion states that “A body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it”. Suppose a block is kept on the floor, it will remain at rest until we apply some external force to it. Also, we know that it takes us more effort or force to move a heavy mass. This is directly related to a property known as Inertia. This law is also known as the law of inertia.

Newton’s Second Law of Motion

The first law has already given us a qualitative definition of force. Now we are interested in finding out its magnitude. According to Newton’s second law of motion, the net force experienced by a body is directly proportional to the rate of change of momentum of the body. It can be written as:

f∝dPdt⇒f∝mv−mut⇒f∝m(v−u)t⇒f∝ma⇒f=kma Where k is the constant of proportionality and it comes out to be 1 when the values are taken in SI unit. Hence the final expression will be,

F = ma

Newton’s Third Law Of Motion

Statement: To every action, there is an equal and opposite reaction.

It means that if a body A exerts a force F1 on a body B, and the body B exerts a force F2 on body A, then

F1=F2 (opposite direction)

According to Newton’s third law of motion, for every action, there is an equal and opposite reaction. Forces are always found in pairs. For instance, when you sit on a chair, your body exerts a force downward and that chair needs to exert an equal force upward or else the chair will collapse.

That is, they are equal in magnitude but opposite in direction.

Whenever two bodies interact, they will exert equal and opposite forces on each other.

This law can be observed anywhere and everywhere in the surroundings. Some of the examples of action-reaction pairs are mentioned below:

1) A swimmer pushes the water backwards by his/her hands and in return the water pushes the swimmer forwards, thus enabling him to go forward during swimming.

2) A man walking on the ground: While walking, a person pushes the ground in the backward direction, and the ground in return pushes the person in the forward direction, thus making him/her to walk.

3) A bird while flying pushes the air downwards with the help of its wings. Consistent with Newton’s third law of motion, the air pushes the bird upwards.

4) When a person is lying on a bed, his weight is opposed by a reaction force from the bed (assuming it must be there because of Newton’s third law of Motion). In turn, both forces cancel each other out, and the person enjoys the equilibrium position.

There are a million more examples of Newton’s third law of motion in our environment. If you observe closely, you can find it anywhere and everywhere.