Newton’s Laws of Motion

Neha Kishor
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Isaac Newton introduced the three basic laws of classical mechanics which describe the relationship between the motion of an object and the forces acting on it. It was in 1687 that he introduced the three laws in his book “Principia Mathematica Philosophiae Naturalis”(Mathematical Principles of Natural Philosophy), which is generally referred to as the “Principia”. By developing his three laws of motion, Newton revolutionized science. 

The first law of motion is stated as follows

 An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force.

In other words, all objects resist a change in their state of motion. Qualitatively, the tendency of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia. This is why the first law of motion is also known as the law of inertia.


  1. When a bus or train starts suddenly, the passengers sitting inside tend to fall backward.
  2.  The dust particles in a blanket fall off when it is beaten with a stick.
  3. When a bus or train stops suddenly, the passengers sitting lean forward.

Newton’s Second Law

Newton’s second law of motion gives the relationship between the force and acceleration. The second law of motion states that:

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.


  1. Kicking a ball-When we kick a ball, we exert force in a specific direction. The stronger the ball is kicked, the stronger the force we put on it and the further away it will travel.
  2. Pushing a cart-It is easier to push an empty cart in a supermarket than a loaded one, and more mass requires more acceleration.
  3. Two people walking-Among the two people walking, if one is heavier than the other, the one weighing heavier will walk slower because the acceleration of the person weighing lighter is greater.

Newton’s Third Law

The third law of motion is stated as follows

Newton’s 3rd law states that there is an equal and opposite reaction for every action.

The third law of motion states that when one object exerts a force on another object, the second object instantaneously exerts a force back on the first. These two forces are always equal in magnitude but opposite in direction. These forces act on different objects and never on the same object.


  1. When a gun is fired, the bullet moves forward (action). The gun recoils backward (reaction)
  2. A book lying on a table exerts a force on the table which is equal to the weight of the book (action force). The table supports the book, by exerting an equal force on the book (reaction). As the system is at rest, the net force on it is zero. Therefore, forces of action and reaction must be equal and opposite

Check your knowledge

Newton’s laws of motion relate an object’s motion to the forces acting on it. In the second law, the force on an object is equal to its mass times its acceleration. In the third law, when two objects interact, they apply forces to each other of equal magnitude and opposite direction.

The Newton’s three laws of motion are Law of Inertia, Law of Mass and Acceleration, and the Third Law of Motion. A body at rest persists in its state of rest, and a body in motion remains in constant motion along a straight line unless acted upon by an external force.

Newton’s First Law:If no net force acts on an object it remains at rest, if initially at rest, or it maintains its velocity if initially in motion. Newton’s Second Law: F = ma: The net force F acting on an object with mass m and acceleration a is given by this expression.

Inertia is a force. Inertia is a force which keeps stationary objects at rest and moving objects in motion at constant velocity. Inertia is a force which brings all objects to a rest position. All objects have inertia.

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