With respect to the vacuum, photons or EM waves travel at the speed of light. With respect to "something other than EM energy" not sure exactly what you mean here. If you are referring to particles or things with mass and look at the equation posted above, as you increase the velocity of the particle its mass starts to increase as the speed approaches the speed-of-light limit. DG

From a totally pratical point yes and I knew how to do that, but I want to actually use the greek letter delta in the assignment, e.g. Δx:=y-z: Thanks, dgiznya

From a totally pratical point yes and I knew how to do that, but I want to actually use the greek letter delta in the assignment, e.g. Δx:=y-z: Thanks, dgiznya

In an attempt to clarify... If I have not changed any of the options on a vanilla install, are there options somewhere that govern when a numeric answer will be converted to scientific notation? for example if I take 1/10 , 1/100, 1/1000, 1/10000 at what point will the answer be displayed as 1x10^x ? lets assume that it diplays .1, .01 ,.001, 1x10^-4 now I know that 10^-4 is the threshold. Is this threshold an option? Can it be changed in preferences? What if I want all my numeric answers in Scientific notation? Is this something that I can change? I assume it is in the precision tab under preferences but the choices there seem very nondescript and I can't find much in the help files on these options. Thanks, dgiznya