Double the speed, quadruple the braking distance

Braking distance goes as the square of speed. Twice as fast is four times the

Why it works

Kinetic energy is a half m v squared, and friction removes it at a roughly constant

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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More in Mechanical

• The bolt-torque shortcutTightening torque ≈ 0.2 × preload × bolt diameter (dry steel).
• Torque mostly fights frictionRoughly 90% of tightening torque is lost to friction; only ~10% actually stretches the bolt.
• Deflection limits: span/250Keep beam deflection under span/250 generally, span/360 where people will notice a bouncy floor.
• Depth beats width, cubedDouble a beam’s depth and its deflection drops 8-fold. Double its width and it only halves.

How far does it take to stop a car?

Braking distance goes as the square of speed. Twice as fast is four times the Kinetic energy is a half m v squared, and friction removes it at a roughly constant .

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