User talk:Tupac Yupanqui

Welcome!

Hello,, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are some pages that you might find helpful: I hope you enjoy editing here and being a Wikipedian! Please sign your messages on discussion pages using four tildes ( ~ ); this will automatically insert your username and the date. If you need help, check out Questions, ask me on, or ask your question on this page and then place  before the question. Again, welcome! Disembrangler (talk) 15:13, 6 June 2009 (UTC)
 * The five pillars of Wikipedia
 * Tutorial
 * How to edit a page and How to develop articles
 * How to create your first article (using the Article Wizard if you wish)
 * Manual of Style

Relativistic mass
Tupac, there are two definitions of mass being used here. One is the invariant mass, which for single particles is the same as the rest mass. The other definition is the relativistic mass, which is NOT invariant, but changes with reference frame, same as total energy. People are always getting confused by the two kinds of mass and the two kinds of energy. Setting c=1, the rest mass (invariant mass) is the same as the rest/invariant energy. And the total energy is the same as the relativistic mass. But these 4 are equal to each other only when total momentum is zero, which means only in the COM frame. It is only there for systems that total energy is equal to invariant mass (and for particles, obviously total energy is rest mass). Anyway, see mass in special relativity for a full discussion of these 4 quantities, only 2 of which are invariant. S B Harris 03:56, 23 December 2009 (UTC)