maximum speed for any object with mass is the speed of light in vacuo. You can't accelerate beyond this as, as you impart more energy to the object, it increase

maximum speed for any object with mass is the speed of light in vacuo. You can't accelerate beyond this as, as you impart more energy to the object, it increases in mass, making it harder to accelerate further. As you approach c the mass tends -> infinite, hence requiring infinite energy to get to c. Objects with no mass on the other hand, all move at c.