Im doing a class assignment and i would like to know the physics behind why anti lock braking system work?

Anti-lock braking systems are designed to operate in such a way as to apply only enough braking force to the rotating wheels to slow them down without allowing them to actually be stopped, which would precipitate a skid.





They do this by continuously monitoring rotational speeds of the wheels, and when one or more start to significantly slow their rotation, the brake pressure is eased to prevent the wheel from locking up (i.e., stopping rotation completely).





Without ABS, the driver would have a tendency to slam down the brakes, preventing the wheels from rotating, with the likely result that the car simply enters an uncontrolled skid along the slippery surface of the road. With ABS, the brakes don't allow the wheels to completely stop rotating thereby giving the driver at least some measure of control on a slippery surface.|||Three rough frictions is better than one smooth friction.


Three Rough frictions are:


1) high pulse brakes, which prevent the car


Wheele from locking with the brakes applied, thus not slipping. By applying brakes and releasing many times a second.


2)when the wheele is turning then the bearings are also turning, that friction is also added to stop the car. It; the


bearing, takes the weight of the car on


itself.


3) friction of the wheele turning on the


ground.





Without all these frictions, as the car slipping, then only #3 applies in different phase; wheele not turning as it slips on the


ground. This one a lone is not as good as


the other three together.|||Brakes are able to stop vehicles because of the friction between the tire and the roadway surface. Before ABS, when the driver pushed hard on the brakes, the wheels easily locked. When the tire provides the same surface to the highway (because it is not turning,) heat builds up and the rubber actually begins to melt. The melted rubber makes little balls and liquifies. The little balls and the liquid rubber provide lubricants so that there is far less friction available to stop the car.





The ABS system senses when the wheel locks up and releases the break for an instant so the wheel and tire can turn providing a fresh, less hot tire with better friction to the roadway.





It is interesting that in the old days good drivers learned to do that same thing, although admittedly not nearly as fast as ABS systems can. Now, I am told if you use the old method with ABS brakes, it is actually less efficient at stopping, you're actually supposed to push the brake as far as it goes and keep it down, something that still feels totally alien to many of us.





I've included below a url where they give a nice step by step explanation of how ABS brakes work.