Will a Car Skid? | Friction and Centripetal Acceleration

[Joe Cruz]

1. A car travels around a circle with a diameter of 500m at a constant speed of 25 m/s. The static friction coefficient is 0.3 and the kinetic friction coefficient is 0.2. Will the car skid?

2. F = ma. F_fr = μmg. Centripetal acceleration = v²/radius3. So the math for this particular problem was really simple, my problem seems to be more of a conceptual one.

The force acting on the car = F = m(25²/250) = m(2.5)
The static friction force = F_sfr = m(.3)(9.8) = m(2.94)
The kinetic friction force = F_kfr = m(.2)(9.8) = m(1.96)

My first assumption is that the car is going to skid since the car is moving and the force acting on the car exceeds the kinetic friction force, but since F_kfr < F < F_sfr, I'm not entirely sure if this is the correct answer. Anyone want to help clarify this problem for me?

 

[AlephNumbers]

What do you think it means to skid? What is the difference in the frictional forces acting on a car that is skidding and those on a car that is not skidding? At what point will a car become uncontrollable and begin to skid?

 

[Doc Al]

Ask yourself: If the car was not to skid, what kind of friction must act?

 

[Joe Cruz]

First, just want to say Mastodon is the dang. Second, I'm assuming skidding means the force acting on the object exceeds the force of friction.

To answer you Doc, I would say the kinetic friction. My problem is that the force of friction is acting perpendicular to the motion of the car itself, and if only the kinetic friction was determining whether the car would skid, why would he include the static friction coefficient as well? Unless it was just there to distract me...

 

[Doc Al]

I'm assuming skidding means the force acting on the object exceeds the force of friction.

What kind of friction?

To answer you Doc, I would say the kinetic friction.

That would be incorrect. Realize that when the tire skids the surfaces are slipping against each other--and that means kinetic friction. So only if skidding occurs will kinetic friction be involved.

My problem is that the force of friction is acting perpendicular to the motion of the car itself, and if only the kinetic friction was determining whether the car would skid, why would he include the static friction coefficient as well? Unless it was just there to distract me...

The force that prevents the car from skidding outward--the force that keeps it moving in a circle--must be static friction. The question is: Is there enough static friction to provide the needed centripetal force?

 

[Joe Cruz]

That would be incorrect. Realize that when the tire skids the surfaces are slipping against each other--and that means kinetic friction. So only if skidding occurs will kinetic friction be involved.

The car being in motion really confused me, but that cleared everything up for me. Thank you.