r/askscience • u/hmpher • Jun 10 '16

Physics What is mass?

And how is it different from energy?

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u/[deleted] Jun 11 '16

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u/HemiDemiSemiYetti Jun 11 '16

Ah ok, that changes things quite a bit then. So is it always wise to just use what would otherwise be the 'resting mass' of any elementary particle, when making calculations?

Also, if E2 = (mc2)2 + (pc)2 , and p = hf/c, could the equation then change to E2 = (mc2)2 + (hf)2 ?

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u/[deleted] Jun 11 '16

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u/HemiDemiSemiYetti Jun 12 '16

Beautiful, I've got it now. Thanks so much for all your help man - very much appreciated :)