• Inertia is a resistance of any physical object to a change in its state of motion or rest.
  • May refer to an objects amount of resistance to change in velocity.
  • Described in Newton's First Law of Motion: an object is no subject to any net external force moves at a constant velocity. (An object at rest to stay at rest, an object in motion to stay in motion.)
  • On the surface of Earth inertia is often masked by the effects of fricition and gravity.
  • Because veloccity includes both the speed and direction of motion, a net force is required to change either the speed or direction of an object's motion.


  • A condition in which all acting influences are cancelled by others, reslulting in a stable, balanced, or unachanging system.
  • *** ´╗┐Example: Two or more individuals siting on a teeter-totter. They weight exactly the same amount and sit exactly the same distance from the center, the teeter-totter will not move. Equilibrium has then been achieved. They will remain at rest until an action takes them out of equilibrium.