Kartdrome

hold to go, slide to steer, let go to brake.

a rental-kart race on the Dubai Kartdrome's International Circuit: steer, brake for the corners at the right moment, and pass ten other karts

A kart turns only as hard as its tyres grip, here about 1.3 g, so every corner has a top speed: the tighter the corner, the lower it is (it goes with the square root of the radius). Brake too late and the kart cannot make the turn: it runs wide over the kerb and into the sand, which costs far more time than braking a few metres earlier would have. The racing line, wide into a corner, clipping the inside, wide out, makes the corner as gentle as the track allows, so it can be taken faster. Close behind another kart you ride in its tow and run a little faster, which is how a pass on a straight is set up. Steering here is helped: while your thumb is turning, an assist does part of the turn, less in each race you play. The layout is the Dubai Kartdrome's International Circuit, traced from its map and scaled to about 1.2 km; the karts' speeds are near a rental kart's, not measured from one.

Concepts: friction, momentum, centripetal-force, timing.

An interactive you play with one thumb, on Wundr.