You’d think it would take twice as far to stop a car going 60 mph than one going 30, but in fact it’ll take about four times as far, roughly 180 feet at 60 mph, versus 45 feet at 30 mph.

It’s an illustration of the principle that as you increase speed, your momentum (and thus your stopping distance) increases exponentially.

In other words, think: an object in motion stays in motion.

Is this right? Momentum is proportional to speed (p=mv) Energy is proportional to speed squared (E=1/2 mv^2), Braking involves dissipating energy into heat so its speed squared that has to be dissipated. Double the speed and you have 4x more energy to dissipate to stop. Work (energy) is force times distance. If the braking force is the same, then 4x the distance when speed is doubled…