Law of the Conservation of Mass, Energy & Momentum

Law of the Conservation of Mass The mass of a body remains
unchanged by any ordinary physical or chemical change to which it may
be subjected.
Law of the Conservation of Energy The principle of conservation
of energy requires that the total mechanical energy of a system remain
unchanged if it is subjected only to forces which depend on position or
configuration.
Law of the Conservation of Momentum The linear momentum of a
system of bodies is unchanged if there is no resultant external force on
the system. The angular momentum of a system of bodies about a fixed
axis is unchanged if there is no resultant external moment about this
axis.