Stopping distance is made up of thinking distance
and braking distance
Both increase as the speed increases
thinking distance increases in proportion to increasing
speed

Thinking distance
(all these things are to with the drive)
drinking alcohol,             taking drugs,
tiredness,          illness,           not concentrating,

Braking distance
(all these things are to do with the car and road conditions)
worn tyres,        poor brakes,         wet roads,
 icy conditions,         oil or grease on the road,   etc.