Newton's Laws of Motion

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Newton's Laws of Motion

Newton's Laws of Motion are one of the Clasic Mechanics sub 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

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 Lawforce 2

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. The unit of force is pound, \(lb_f\) or Newtons.

Newton's Second Law Formula

\( F = m   a \;\) if the object is free fall with on other force other than gravity.


\(F\) = force

\(m\) = mass

\(a\) = acceleration

Solve for:

\( m = \frac {F}{a}\)

\( a = \frac {F}{m}\)

Rotational Newton's Second Law Formula

\( \tau = I  \alpha  \)


\(\tau\) (Greek symbol tau) = rotational force

\(I  \) = moment of inertia

\(\alpha\) (Greek symbol alpha) = angular acceleration

Newton's Third Law

Also known as the "Law of Actions and Reaction".  For every action there is an equal and opposite reaction.

Newton's Third Law Formula

\(F_1 = -F_2\)


\(F\) = force

Tags: Equations for Force Equations for Motion