Mass defect

Mass defect

Mass defect (also called "mass deficit") is the difference between the mass of an object and the sum of the masses of its constituent particles. Mass defect can be explained using Albert Einstein's formula E = mc, published in 1905, which describes the equivalence of energy and mass. The decrease in mass is equal to the energy emitted in the reaction of an atom's creation divided by c. By this formula, adding energy increases mass (both weight and inertia), whereas removing energy decreases mass. For example, a helium atom containing four nucleons has a mass about 0.8% less than the total mass of four hydrogen atoms (each containing one nucleon). The helium nucleus has four nucleons bound together, and the binding energy which holds them together is, in effect, the missing 0.8% of mass.