## Conceptual Physics (12th Edition)

At half the speed of light, v/c = 1/2, measurements of time intervals differ by a factor 1.15. At $99.5\%$ of the speed of light, v/c = 0.995, measurements of time intervals differ by a factor of 10.
$$\gamma = \frac{1}{\sqrt{1-0.5^{2}}} = 1.15$$ $$\gamma = \frac{1}{\sqrt{1-0.995^{2}}} = 10.0$$ This is discussed on page 666.