Thomson’s slightly complicated result depended on the object’s charge, radius and magnetic permeability, but in 1889 English physicist Oliver Heaviside simplified his work to show that the effective mass should be m = ( 4⁄ 3) E / c 2, where E is the energy of the sphere’s electric field. Thomson understood that the field of the sphere should act like the air before the beach ball in his case the effective mass of the sphere was the entire mass induced by the magnetic field. The “effective” mass of the falling beach ball is consequently larger than the mass of the ball at rest. Drag or no drag, in order to fall the ball must push the air ahead of it out of the way and this air has mass. The force of gravity pulls the ball downward buoyancy and drag forces from the air impede the ball’s fall. The effect is entirely analogous to what happens when you drop a beach ball to the ground. Thomson, later a discoverer of the electron, made the first attempt to demonstrate how this might come about by explicitly calculating the magnetic field generated by a moving charged sphere and showing that the field in turn induced a mass into the sphere itself. Late 19th-century natural philosophers believed that electromagnetism was more fundamental than Isaac Newton’s laws of motion and that the electromagnetic field itself should provide the origin of mass. Hence, moving charged particles carry electromagnetic fields. Einstein was neither the first person to consider the equivalence of mass and energy, nor did he actually prove it.Īnyone who sits through a freshman electricity and magnetism course learns that charged objects carry electric fields, and that moving charges also create magnetic fields. Energy and mass are the same.Īccording to scientific folklore, Albert Einstein formulated this equation in 1905 and, in a single blow, explained how energy can be released in stars and nuclear explosions. ![]() If we think of c, the speed of light, as one light year per year, the conversion factor c2 equals 1. ![]() ![]() Yet E = mc 2 tells us something even more fundamental. The equation’s message is that the mass of a system measures its energy content. Indeed, the immortal equation’s fame rests largely on that utter simplicity: the energy E of a system is equal to its mass m multiplied by c2, the speed of light squared. No equation is more famous than E = mc 2, and few are simpler.
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