# Laws of Motion: What is Inertia, What is Force, What Are Newton՚s Laws of Motion (For CBSE, ICSE, IAS, NET, NRA 2022)

Get unlimited access to the best preparation resource for competitive exams : get questions, notes, tests, video lectures and more- for all subjects of your exam.

## What is Inertia?

• The property of an object by virtue of which it cannot change its state of uniform motion along a straight line or rest on its own is called as inertia.
• Inertia is the resistance of any physical object to any change in its velocity. This includes changes to the object՚s speed, or direction of motion.
• It is the measure of the mass of a body.
• An aspect of this property is the tendency of objects to keep moving in a straight line at a constant speed, when no forces act upon them.

There are 3 types of inertia:

• Inertia of rest
• Inertia of motion
• Inertia of direction

## What is Force?

• A force is a push or pull upon an object resulting from the object՚s interaction with another object.
• In physics, a force is any interaction that, when unopposed, will change the motion of an object.
• A force can cause an object with mass to change its velocity, i.e.. , to accelerate.
• It can also be described intuitively as a push or a pull.
• A force has both magnitude and direction, making it a vector quantity.

Force can be categorized into two types:

• Constant Force
• Action at a distance force

## What is Newton՚s Laws of Motion?

• In classical mechanics, Newton՚s laws of motion are three laws that describe the relationship between the motion of an object and the forces acting on it.
• The first law states that an object either remains at rest or continues to move at a constant velocity, unless it is acted upon by an external force.
• First Law: “A body continues in its state of rest or of uniform motion in a straight line unless it is compelled by some external force to change that state.”
• Newton՚s first law 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 force.
• This is normally taken as the definition of inertia. The key point here is that if there is no net force acting on an object then the object will maintain a constant velocity.
• If that velocity is zero, then the object remains at rest. If an external force is applied, the velocity will change because of the force.
• Second Law: “The net force produced by an object is directly proportional to the magnitude of the net force and takes place in the direction of the force.”
• The second law explains how the velocity of an object changes when it is subjected to an external force.
• The law defines a force to be equal to change in momentum (mass times velocity) per change in time.
• Newton also developed the calculus of mathematics, and the “changes” expressed in the second law are most accurately defined in differential forms.
• For an object with a constant mass m, the second law states that the force F is the product of an object՚s mass and its acceleration a:

• Third Law: “To every action, there is an equal and opposite reaction.”
• The third law states that for every action (force) in nature there is an equal and opposite reaction. In other words, if object A exerts a force on object B, then object B also exerts an equal force on object A.
• Notice that the forces are exerted on different objects.
• Third law can be used to explain the generation of lift by a wing and the production of thrust by a jet engine.

Developed by: