# Friction and drag in cars

Drag is a problem for all vehicles. As the vehicle moves forwards through the air the air rushes past the vehicle. This causes friction, which we call drag, and this slows the vehicle down. Large amounts of money are spent by the designers of cars to try and make a car which has a little drag as possible.

Newton's second law tells us the acceleration of an object when a force is applied but this force must be the net force.

In other words if the engine of a car gives it a thrust of 2000 N but the frictional drag is 200 N then the net force left to accelerate the car is only 2000 – 200 = 1800 N.

If the drag equals the thrust there would be no net force and the car would stop accelerating.

The drag due to the friction of the air gets bigger the faster you go and so reducing this is particularly important for high speed cars such as racing cars.

Friction between racing car tyres and the track is vital. The "normal" racing tyres are called slicks, they have hardly and tread and so top help them grip the tyres are warmed up before a race. This can be done by slewing the car backwards and forwards across the road in the practice lap and by keeping the tyres in a kind of electric blanket until they are put on the car. Due to this heating the rubber melts a bit so that they literally stick to the road.

This is fine until it rains!

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