## Physics: Principles with Applications (7th Edition)

The relativistic formulas are valid for all speeds, but only for speeds close to the speed of light do we notice the effects of time dilation, length contraction, and change in mass. The value of $\gamma$ is $\frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$, and that is basically equal to 1 for all intents and purposes unless $\frac{v}{c}$ is at least a few fractions of a percent.