Pretty straight-forward, I'm just curious. My current level and understanding of physics has lead me to believe that as an object accelerates it's mass becomes higher and if it were to be able to reach the speed of light it would get infinite mass. I believe this currently, however, two of my friends have denied this statement saying that, rather, an object's mass will become zero when it reaches the speed of light. I'm just wondering if I'm correct or if they are. If they're correct, is it just a simple misunderstanding, or mistake on my part, or is it that I don't understand physics to the correct level to attempt to understand this yet? Thanks for anyone who can respond to this, and please have a nice day!