Why speed quadruples your braking distance.

Braking distance follows d = v²/(2μg), from Newton's laws under constant deceleration μg — see Braking distance. In this tire-friction-limited model, both kinetic energy and available friction force scale with mass, so mass cancels from distance; it still scales the kinetic energy that must be dissipated. The reaction slider spans a roughly 0.2 s laboratory simple-response benchmark (not real hazard perception) to the 2.0 s value sometimes used for elderly or inexperienced drivers; 1.5 s is a common crash-reconstruction baseline. See mental chronometry and the reaction-time discussion in total stopping distance. Distance comparisons use a 50 m Olympic-size pool, a 105 m football pitch, and one 400 m lap of a standard running track. The running-energy comparison assumes a 70 kg person and about 1 kcal/kg/km on level ground, a rough metabolic cost supported by Margaria et al. Real cars vary with tires, slope, aerodynamics, brake capacity, ABS, and heat; regenerative braking may recover some energy instead of dissipating it as heat.