I read somewhere than whenever we increase the velocity of a particle, the mass of he particle also increases. I also read that it is impossible reach the speed of light as the mass of the particle, just before reaching the speed of light, will become infinite (not infinite but very large) and a lot of force will be needed to increase the speed further which will only result in more increase in mass. Now, i have the following 2 questions- 1. Why do mass go on increasing? and- 2. what if we consider mass less particles? Which there will an increase in mass too? If no, then why cant they achieve the speed of light?