When a car is moving on a road without applying the brake, the tyres are rolling on the ground and no significant mark will be left on the road. Once the brake is applied, the wheels are locked without rolling and the tyres will slip on the road causing skid marks on the road surface. The length of the skid marks begins when the brake is applied and ends when the car stops. Actually, it is the friction between the tyres and the road surface that causes the car to decelerate and stop. The following experiment allows you to investigate the relationship between the friction of an object and its weight.ExperimentPlace a wooden board on a rough surface, add several weights on the wooden board. Then attach a spring balance to the wooden board and pull the wooden horizontally (Figure 1). Observe and record the reading on the spring balance when the board JUST starts to slide on the rough surface. This is the frictionbetween the wooden board and the rough surface