# Newton's Laws of Motion

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Newton's laws of motion is one of the Clasical branches in physics.  These three laws show the relations between the forces acting on a body and the motion of the body.

## Newton's First Law

Newton's first law, also known as the Law of Inertia, a object at rest remains at rest and a object in motion continues to move at a constant velocity unless acted upon by an external force.

## Newton's Second Law Newton's second law, also known as the Law of Resultant Force, is the force that causes an object or mass to accelerate.  The greater the mass to be accelerated, the greater the force required to move the mass.

## Newton's Second Law formula

$$\large{ F = m \; a }$$     (if the object is free fall with on other force other than gravity)
Symbol English Metric
$$\large{ F }$$ = force $$\large{lbf}$$  $$\large{N}$$
$$\large{ a }$$ = acceleration $$\large{\frac{ft}{sec^2}}$$ $$\large{\frac{m}{s^2}}$$
$$\large{ m }$$ = mass $$\large{lbm}$$ $$\large{kg}$$

## Newton's Second Law for Rotation Formula

$$\large{ \tau = I \alpha }$$
Symbol English Metric
$$\large{ \tau }$$  (Greek symbol tau) = rotational force $$\large{ lbf-ft }$$    $$\large{ N-m }$$
$$\large{ I }$$ = moment of inertia $$\large{ in^4 }$$  $$\large{ mm^4 }$$
$$\large{ \alpha }$$  (Greek symbol alpha) = angular acceleration $$\large{ \frac{deg}{sec^2} }$$  $$\large{ \frac{rad}{sec^2} }$$

## Newton's Third Law

Newton's third law, also known as the Law of Actions and Reaction, is for every action there is an equal and opposite reaction.

## Newton's Third Law Formula

$$\large{ F_1 = -F_2 }$$
Symbol English Metric
$$\large{ F }$$ = force $$\large{ lbf }$$  $$\large{ N }$$ 