What is mass? Does it change with speed? Mass is the total energy contained in the body when it is in rest (definition given by the famous equation E=mc^2). Mass donot change when the speed changes but the energy is changed as we have to take the motion (momentum) into account. The total energy then becomes E=[(mc^2)^2+(pc)^2]^0.5. Some fabulous writer of 19th century (Pauli, Born etc) wrote that mass of body itself change when speed changes. But we now donot use the equation of rel. Mass these days. We see everything in terms of Energy-momentum relation which shows mass is a frame independent lorentz scalar as:- E^2-(pc)^2=(mc^2)^2=E^2-(pc)^2 The century old equation of relativistic mass gives not the increased mass but gives the total energy of the body. The equation for rel. Mass and Energy-momentum are equivalent. But care should be given while interpreting the result. I made the post to Settle some repetitive debates. Here are some answers to repetitive questions. *Photon is massless whatsoever be its state of motion. Some say photon do have mass when it moves but that is fallacious. *Now there is another question:- why object cant go beyond c. Well see from energy-momentum relation:- the faster it moves the more energy it does have. So it needs more and more energy to accelerate it. Even a small massive point cant be accelerated to c even if you use the total available energy of the entire universe to it alone.
Posted on: Sun, 28 Sep 2014 00:31:44 +0000
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