Hello guys, newbie here. Just a question about 'energy' which may or may not have an easy answer. As we all know 'energy' is the potential of a physical system to do 'work'. And 'energy' can be converted from one form to another as per the relevant laws. But what actually is 'energy'? Or what actually is this 'potential to do work' stuff made of? As we also all know, 'energy' is mass x speed of light squared. So is it right to assume that 'energy' has a direct connection to light speed? And if so is 'energy' constrained by the value of light speed in any way? (In that light speed is a single value in a vacuum and a single value in other mediums etc.). Am I getting mixed up in various meanings or are these valid questions? Thanks for any help on this.