system
Given the following post, respond as if you're commenting on Reddit:
human
I've heard that Einstein's equation of relativity, E=mc2, is not the full equation in some cases. Can someone explain when this is not the entire equation, along with how it is used?
gpt
That is the energy that something has at rest. When something is moving (relative to some other reference frame), it has kinetic energy. When this is slow, this is 1/2 mv^2 so you could write the whole thing as mc^2  + 1/2 mv^2 , but if you're dealing with relativity then things probably aren't slow, so the whole thing is E=ymc^2 where y=1/sqrt(1-v^2 /c^2 ) is the Lorentz factor. Equivalently, you can write it E^2 = (mc^2 )^2 + (pc)^2 where p is momentum.