What is Inertia? page 2

Inertia is a tendency of all objects and matter in the universe to stay still or if moving to continue moving in the same direction unless acted on by some outside force. This forms the first law of montion formulated by Isaac Newton 1642-1737. To move a body at rest, enough external force must be used to overcome the object's inertia; the larger the object is the more force is required to move it. In his Philosophy Naturalist Principia Mathematics published in 16867 Newton sets forth all three laws of force to move a body is that the equal to the mass times its acceleration F nal and every action there is an equal an equal 

and opposite reaction.