## Conceptual Physics (12th Edition)

Let $L_{o}$ represent the original, rest length of the car, and L the measured length of the moving car. $$L = L_{o} \sqrt{1-\frac{ v^{2} } { c^{2} }}$$ This is discussed on page 676. For ordinary speeds, even 200 mph, the difference is not measurable, less than an atomic diameter. On the other hand, for speeds that are appreciable compared to the speed of light, the decrease in length is substantial.