and another question,is it true the closer towards to the speed of light an object is travelling the more mass it gains?if this is true where does this extra mass come from and does this mean that an object travelling at light speed has infinate mass?surely an object with infinate mass would engulf the entire universe...sorry another strange question i know.
Phew....all I know is my kitchen light has fused (Y always at night) to change it I have to climb on a chair, unscrew 4 screws, remove glass cover, get off chair to place cover on table, climb back on chair to remove old bulb & insert new, off chair to put fused bulb down. Wash glass cover, dry, climb on chair and hold cover in place carefully with one hand while other hand feels for screw-driver and screw it all back. Down off chair, switch on......voila! DTH?
sandman - yes that is all true. The mass comes with the energy you apply to the object. E=mc^2 and all that. You would need to convert all the mass in the universe to energy (except your object of course). Then use the energy to accelerate your object. And you still wouldn't reach light speed.
And in fact, objects moving at the speed of light are effectively massless. Photons, for example, are massless.
As eltelioni says, the mass is due to the mass energy conversion. Mass and energy are really the same thing. The more energy you put into the system, the more mass it gets.
But note that you can keep pushing and pushing, and the object will get faster and heavier. But it'll never get to the speed of light. Just 99.99% the speed of light, etc. So you'll never have something with infinite mass.
In fact Einstein's relationship tells us more, it says Energy and mass are interchangeable. Or, better said, rest mass is just one form of energy. For a compound object, the mass of the composite is not just the sum of the masses of the constituents but the sum of their energies, including kinetic, potential, and mass energy. The equation E=mc2 shows how to convert between energy units and mass units. Even a small mass corresponds to a significant amount of energy.