Energy is Equivalent to Mass 1:1  Special Relativity as a Tool 1:1 » 
Energy is Equivalent to Mass 

Energy and mass are related to each other by the wellknown formula E_{0}= mc^{2}, where E_{0} is the rest energy, m is the mass, and c is the speed of light in vacuum. This means that mass and energy are equivalent. The 'effective' mass M of an object moving relative to an observer at rest is given by where E is the energy of the object and m is the mass of the object. This formula is called the relativistic mass formula.
