ABSTRACT
In this chapter we shall consider experiments that show that at very high speeds, close to the speed of light, Newtonian mechanics is completely inadequate. For example, in Section 2.5 an experiment will be described which shows clearly that there is a limiting speed for accelerated electrons, which is equal to the speed of light in empty space, whereas, according to Newtonian mechanics, the speed of an accelerated electron should increase continuously towards infinity. It will be shown in this chapter that if momentum is redefined using equation (2.1) then it is possible to develop a new theory for the motions of high-speed electric charges in electric and magnetic fields that is in excellent agreement with the experimental results. This new theory is generally called relativistic mechanics. The adjective “relativistic” is often used to describe quantities appropriate to particles moving at speeds close to the speed of light. For example, a particle moving at a velocity close to the velocity of light is often said to be moving at a relativistic velocity. Some of the implications of assuming that the new experimentally confirmed laws of relativistic mechanics obey the principle of relativity will be discussed in Section 2.13, where it will be shown that the Galilean transformations must be replaced by the Lorentz transformations. A full discussion of relativistic mechanics is given in Chapter 6.
