Richard Feynman scrive riguardo al Secondo Principio della Dinamica di Newton nel suo trattato „Lectures on Physics“ (Capitolo 15):

For over 200 years the equations of motion enunciated by Newton were believed to describe nature correctly, and the first time that an error in these laws was discovered, the way to correct it was also discovered. Both the error and its correction were discovered by Einstein in 1905.

Newton’s Second Law, which we have expressed by the equation

$F=d(mv)/dt$

was stated with the tacit assumption that m is a constant, but we now know that this is not true, and that the mass of a body increases with velocity. In Einstein’s corrected formula m has the value

$m=\frac{m_0}{\sqrt{1-v^2⁄c^2}}$

where the rest mass  represents the mass of a body that is not moving and c is the speed of light […]”. Fine della citazione.

Infatti, se la massa m nell’equazione della seconda legge della dinamica è sostituita dalla formula della massa relativistica dipendente dalla velocità, differenziando si ottiene l’espressione dell’accelerazione relativistica (vedi dimostrazione).

Il testo di Richard Feynman prosegue con l’affermazione:

For those who want to learn just enough about it so they can solve problems, that is all there is to the theory of relativity-it just changes Newton’s laws by introducing a correction factor to the mass.”

Questo è proprio quello che descriviamo su questo sito (vedi “Sequenza di dimostrazioni relativistiche“).