Solving Friction Problems: Why Only Static Friction Applies?

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In summary, the conversation discusses the concept of static friction in relation to a car's ability to stop on a rainy day. The coefficient of static friction between the road and tires is given, and this value is used to calculate the minimum distance the car will stop. The conversation also addresses the difference between static and kinetic friction and how ABS can play a role in maintaining static friction.
  • #1
grief
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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.
 
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  • #2
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.
 
  • #3
so does that mean, when I press the breaks, there is only static friction between the tires and the road?
 
  • #4
With (an ideal) ABS, I suppose, there's only static friction(?)
 
  • #5
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.
 
  • #6
ohh, ok, I get it now. Thank you for the help
 

1. What is friction and why is it important to understand?

Friction is the force that resists the relative motion between two surfaces in contact. It is important to understand because it affects the movement and stability of objects and is present in many everyday situations.

2. What is the difference between static and kinetic friction?

Static friction is the force that keeps an object at rest, while kinetic friction is the force that opposes the movement of an object.

3. Why does only static friction apply in some situations?

In certain scenarios, the force required to overcome static friction is greater than the applied force, thus preventing the object from moving. This is why only static friction applies in these cases.

4. How do I calculate static friction?

Static friction can be calculated using the formula Fs = μsN, where Fs is the static friction force, μs is the coefficient of static friction, and N is the normal force between the two surfaces.

5. How can I reduce static friction?

Static friction can be reduced by using lubricants, polishing the surfaces, or by increasing the surface area of contact between the two objects. Additionally, reducing the weight of the object can also decrease the force of static friction.

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