Friday, December 2, 2011

I need help with this physics question please?

I don't know this at all, and I would appreciate any type of answer to help me. Thank you in advance.





Most new cars come equipped with ABS (anti-lock braking system) that keeps the tires from "locking up" when you press on the brakes. They accomplish this by causing the brakes to engage and disengage about 30 times a second (equivalent to someone "pumping" the brakes very quickly. Why do you think it is that a car will come to a stop over shorter distances when the tires do not skid?|||There are two reasons. The first is that the 'starting friction' is usually higher than the 'sliding friction'. Once something starts to slip, it takes less force to keep it moving than it took to start it sliding. So the sliding tire exerts less force on the road than one that is just about to start sliding.





The other reason (possibly not relevant to your teacher) is that when a tire slips, the generated heat causes the rubber to actually melt onto the road, which provides a liquid interface between the tire and the road, reducing friction even further. This is the principle of how an ice skate works; the pressure of the skate melts the ice slightly, which makes it slide very easily.|||More energy is dissipated through efficient brake systems than is through friction of skidding tires.|||It's because the force of friction between the tires and the road can be greater when there is no slipping of the tires along the surface. Static friction can exceed kinetic friction. So it is best to try to maximize the braking force by making it as large as possible before slipping begins.





I always thought that ABS sensed when slipping began (that is, when the tire quits rotating) and then backed off on the braking force until it starts rotating again.





I'm not so sure that's the way it works. My 2002 Prius has ABS and I'll swear I can stop that thing quicker by careful control of the brake pedal. I'm starting to wonder how good the ABS system I have really is...|||Static friction is greater than kinetic friction.... Static friction occurs when the wheels are turning and not slipping on the pavement. So if the tires lock up and are sliding across the pavement, kinetic friction is occuring and the car is not going to stop as quickly.

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