More Relativistic Effects

What happens to an object when it travels very fast, perhaps approaching the speed of light?

We have seen that time, for the object, runs at a different rate. Unstable particles with a certain half life seem to last much longer when they are moving quickly.

Distances are shortened.

The mass of objects also changes. No object can be accelerated to the speed of light. If we were to keep accelerating a very fast moving object, e.g. in a particle accelerator, its kinetic energy will increase but rather than gain velocity it will gain mass ( as kinetic energy = ½ m v² ). Einstein showed that mass and energy are transferable which is summarised by his famous equation E = m c²

If an object is not moving we say it has a rest mass. The rest mass of a proton for example is 9.11 x 10^-27kg. If we accelerate the proton, e.g. we give it 5GeV of energy (5 x 10⁶ x 1.6 x 10^-19J), its mass increases significantly.

Later on this course we will use the relativistic equation  p = E/c to calculate the momentum of fast moving particles, from which we can calculate several interesting things.