why does an object gain mass as it approaches c?

Question

has there been any empirical evidence to support this notion or is it proven in equations only?

ok, I'll accept that it has been measured,but do we know why?or where the extra mass comes from?

Answer 1

No, we do not know why.
The Newtonian formula for the kinetic energy of mass is E=1/2MV^2. If we set the velocity to zero, the energy of the mass also becomes zero. We know now that this isn't true - mass and energy are equivalent.
Einstein developed his formula based on the premise that the speed of light was constant for all observers, irregardless of their relative motions. His formula for the energy of mass was E=MC^2/sqrt1-V^2/C^2. (This formula "simplifies" and "substitutes" and "combines" to E=sqrtM^2C^4+P^2C^2 and on to the famous E=MC^2)
The formula has stood the rigorous testing of modern technology and has given the correct results obtained by actual experimentation.
As you can see, at speeds approaching those of light, the energy increases dramatically - at light speed, it becomes a fraction with a huge numerator (MC^2) and a zero in the denominator (since the amount is increasing steadily as we increase speed closer to that of light, some believe this indicates an infinite energy level, hence, an infinite mass.)
This is the reason that according to relativity theory, the speed of light is the universal speed limit. A speed which cannot be attained by any object.
Again, as to WHY? - I guess I would have to say because the phenomenon is directly related to the mathematics in the formula. It is simply the way the universe works.

Answer 2

The mass of an object does, in fact, increase at relativistic speeds. It's been measured thousands of times in particle accelerators in Physics Departments all over the World.

Doug