The Player Car

The interceptor sits on the road like a picture of a car. Press W and nothing happens. And a car is not a walking character: press left on a walker and it steps left, but press left in a car and only the nose turns.

Nose and momentum

Turn the wheel and the nose turns. The momentum does not. The car keeps going the way it was going, and the tyres drag it round to the new nose. While they work, the nose and the travel point different ways. That gap is a slide.

So every frame, the game splits the car's velocity (its speed and direction together) in two: the part along the nose, and the part sideways. The pedals work on the first part. Grip works on the second, and all it can do is shrink it:

new slide  =  old slide × (1 − grip) to the power of (dt / 0.1)

dt is the seconds since the last frame, about 0.017 at 60 frames a second. grip is the share of the slide the tyres scrub off every tenth of a second. Start with a 10 m/s slide and wait 0.1 s:

grip 0.9    1 m/s of slide left
grip 0.3    7 m/s left
grip 1.0    0 m/s left: the car runs on rails