This page is from a section entitled “Equations of Motion of the Material Point.” Einstein shows how the most basic freshman-physics equations must change to fit the new world.

In the bottom paragraph, *m* is an object’s mass *q*; its speed, and *c *is the speed of light in the vacuum. The text, continuing on the next page, reads: “The expression within the brackets on the right plays the role of the energy *E *of the moving mass point. This expression: [formula 28] grows to infinity when *q *approaches the value *c*; thus, it would require an infinite expenditure of energy to impart the velocity *c *to the body.

That is why even today’s highest-energy particle accelerators can only push particles to approach—but never equal or surpass—the speed of light.

The old Newtonian formula, gives zero if *q *is zero. Here, for *q=0 *the formula reduces to a special case, called rest energy:*E=mc ^{2}*.