Inertia is a non-quantifiable property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the motion of matter and how it is affected by applied forces. Today, it is most commonly defined using Sir Isaac Newton's first in Philosophiae Naturalis Principia Mathematica which states: In common usage, however, peop