Howcome according to theory of relativity when a object moves close to the velocity of light it shrinks in....

Question

Howcome according to theory of relativity when a object moves close to the velocity of light it shrinks in size even though it gains mass?

Answer 1

All the weird effects predicted by relativity result from the fact that if I'm standing still on a platform and you're in a train moving at a steady speed past me, we both measure the speed of a light beam to be the same; about 300 000 km/second. This goes against our everyday experience; If I throw a brick at your train as it moves away from me, it hits the train at the speed it left my hand minus the speed of the train, but this simple relationship breaks down for very fast-moving things like a light beam. So if your train is moving fast enough, two events which I judge to be simultaneous seem to you to happen at different times. You appear to me to be squashed-up in the direction you're moving, your mass appears to increase and your watch slows down. And you judge that the same things are happening to me. According to classical physics, when you slow down and stop, you have no kinetic energy. According to relativity, you've still got a huge amount of energy even when you've stopped moving. If you put energy into something by making it hotter, or by charging a battery or making it spin round, its mass increases. If you burn a piece of coal, the ash and waste gases weigh a little bit less than the coal and air before combustion because of the energy that's been lost.