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

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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?

Newtons 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.

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