The
total energy of a
body of mass m is given by
E = γmc2
where
total energy = kinetic energy + rest energy
or..
E = KE + E0
When a body is at rest γ = 1, KE = 0 and the rest energy E0 is given by
E0 = mc2
The rest energy includes all forms of energy internal to the system.
The kinetic energy of a body of mass m is
KE = γmc2 - mc2
If the speed of the object is not too large, this reduces too the usual expression
KE = ½mv2 ( v << c )
Using the expression p=γmv, the total energy of a body can be written as:
E2 = m2c4 + p2c2