Conservation

1. The act of preserving, guarding, or protecting; the keeping (of a thing) in a safe or entire state; preservation.
   
Conservation of areas (Astron.),
the principle that the radius vector drawn from a planet to the sun sweeps over equal areas in equal times.
Conservation of energy, or Conservation of force (Mech.),
the principle that the total energy of any material system is a quantity which can neither be increased nor diminished by any action between the parts of the system, though it may be transformed into any of the forms of which energy is susceptible.