Solving Friction Problems: Why Only Static Friction Applies?

[grief]

The question is:

A car is traveling at 50 mi/h on a horizontal highway. If the coefficient of static friction between road and tires on a rainy day is 0.10, what is the minimum distance in which the car will stop?

I know how to solve it using static friction, but I don't understand why only static friction is needed in the problem, and kinetic friction does not apply.

 

[Jameson]

What is static friction? A force which prevents any relative motion until its threshold is reached. So in order to keep the friction between the road and your tires, you must maintain a minimum acceleration. And once you find this acceleration, you can find the minimum distance it will take to stop.

 

[grief]

so does that mean, when I press the breaks, there is only static friction between the tires and the road?

 

[Päällikkö]

With (an ideal) ABS, I suppose, there's only static friction(?)

 

[Integral]

That is correct, as long as your wheels are not skidding they maintain static friction with the road. Consider the difference between skidding and rolling.

 

[grief]

ohh, ok, I get it now. Thank you for the help