Newton's laws of motion

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Newton's laws of motion

Newton, the father of physics established the laws of motion in his book "principia" in 1687.

Newton's first law of motion

Every body maintains its initial state of rest or motion with uniform speed on a straight line unless an external force acts on it.
» First law is also called law of Galileo or law of inertia.
» Inertia : Inertia is the property of a body by virtue of which the body opposes change in its initial state of rest or motion with uniform speed on a straight line.
» Inertia is of two type - Inertia of rest and Inertia of motion.
» First law gives the definition of force.

Force is that external cause which when acts on a body changes or tries to change the initial state of rest or motion with uniform velocity of the body.

Momentum is the property of a moving body and is defined as the product of mass and velocity of the body. i.e. momentum = mass * velocity.
» It is a vector quantity. Its SI unit is kgm/s.

Newton's second law of motion

The rate of change in momentum of a body is directly proportional to the applied force on the body and takes place in the direction of force.

F = m a
Where, F = force applied, a = acceleration produced and m = mass of body

» Newton’s second law gives the magnitude of force.
» Newton’s first law is contained in the second law.

Newton’s Third law of Motion

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

Principal of conservation of linear momentum

If no external force acts on a system of bodies, the total linear momentum of the system of bodies remains constant
As a consequence, the total momentum of bodies before and after collision remains the same.
» Rocket works on the principle of conservation of linear momentum.

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