Key concepts
During braking, the tire contact patch pushes forward on the road and the road pushes backward on the tire. The maximum usable grip is approximately friction coefficient × normal force.
Thinking distance grows directly with speed and reaction time. Ideal braking distance grows with speed squared, so doubling speed makes braking distance about four times larger on the same level surface.
Applications and misconceptions
Safe following gaps allow for perception, reaction, and braking. Wet roads reduce grip; worn tires increase hydroplaning risk; downhill gravity lengthens stopping distance.
Misconception: a heavier car does not automatically have a longer ideal friction-limited stop on a level road because both friction and inertia scale with mass. Real brakes, tires, heat, and load transfer can still make mass important.