When a speedy bus stops suddenly, why does it slip a bit forward? There are two reasons why a bus may skid on the roads, firstly due to high speed and secondly, when the friction between the tire and the road has been reduced due to oil leakages from other vehicles, natural weather conditions like snow or due to wear and tear of the tires. Lets discuss every possibility separately; Skidding due to high speed: Buses are of 3 types, mini, midi and coaches. The minibuses seat up to 15 passengers, midi has 16 to 29 seats and coaches can comfortably seat up to 60 people. Irrespective of their size, every bus weighs more than a tonne i.e. more than 1000 kgs or 2200 lbs. For example the average weight of a minibus can be between 3 to 5 tonnes, depending of the number of features and equipment in the vehicle. Midi and coaches will obviously weigh more due to their larger size. Moreover, 15 passengers can easily add another ton of weight to the bus with their luggage included. The total weight of a fully occupied minibus can go up to 6 tonnes. Lets, re-imagine the bus as a rectangular box that weighs approximately 6 tonnes. If this box had 4 tires and was speeding down the highway, then its weight would start gathering momentum due to the gravitational pull of the earth. To understand this concept, you need to understand the difference between potential energy and kinetic energy.