# Shouldn't this be kinetic friction instead of static friction!?

The concepts of rolling resistance, kinetic friction and static friction for a rolling wheel is a hot topic!In summary, the car is moving in one direction and skidding/not-skidding in another direction.f

Homework Statement
Shouldn't this be kinetic friction instead of static friction!?
I know how to solve the problem but the thing is I'm confused!
I think that it must be Kinetic friction because the car is moving
I hope you understand my point!
Relevant Equations
F_s =u_s*N

In what direction is the car moving ? In what direction is the car skidding/not-skidding ?

In what direction is the car moving ? In what direction is the car skidding/not-skidding ?
What I'm asking about is why is STATIC FRICTION not KINETICK Friction?

Homework Statement: Shouldn't this be kinetic friction instead of static friction!?
I know how to solve the problem but the thing is I'm confused!
I think that it must be Kinetic friction because the car is moving
Kinetic friction occurs when two surfaces slide over each other; there must be relative motion between the two surfaces in contact. When a tyre rolls, there is no sliding between the rubber and the road (unless wheelspin or a skid occurs).

It is useful to think about what would happen if the car going in a circle hit a patch of perfectly smooth ice (where there is no friction).

MatinSAR
Just because an object is moving does not mean that kinetic friction is necessarily at play.

Place a small book on flat table. Push hard down on the book with your hand and move your hand horizontally so that the book slides across the table. Both static and kinetic forces of friction act on the moving book. Static between your hand and the book because the book and your hand do not move relative to each other; kinetic between the book and the table because the book and the table move relative to each other.

How does this difference between the two apply here?

nasu
First time studying friction so be patient on me please.
So if a car is using a handbrake on road it has Kinetic friction?
And if it is moving on a road with curve it has static friction and no kinetic friction at all?

Skidding tires are under the influence of kinetic friction. Rolling (but not skidding tires) are under the influence of static friction.

When a rear-wheel drive car accelerates so quickly that the rear tires are smoking, which type of friction is in play for the front tires? For the rear tires?

https://www.redbull.com/ca-en/what-is-drifting-guide

malawi_glenn
I am sure that for the front tires it's static
for the rear im taking only a guess that its also static? Cause they are rolling?
Still having hard time imagining it.

The rear tires are skidding/slipping, so that would involve kinetic friction.

It's the same for locking up the brakes and skidding to a stop, and for doing a burn-out with lots of power to the tires -- in both cases the tire surface rubber is sliding against the roadway, not rolling smoothly with it. Does that help?

PeroK
It's the same for locking up the brakes and skidding to a stop, and for doing a burn-out with lots of power to the tires -- in both cases the tire surface rubber is sliding against the roadway, not rolling smoothly with it. Does that help?
I have got it now thank you for your time.
Man I love this site!

malawi_glenn, PeroK and berkeman
Where we have ice and snow in winter, tires generally have slightly lower dynamic friction than friction on ice. So when stuck on icy & snow, it is important not to spin the wheels fast which many unskilled drivers tend to do. Rather the solution is to rock the momentum of static forces in forward and reverse until you travel to better traction surface. Studded tires can offer more dynamic friction but damage highways with high volume of track so only salt and sand are used, spread by trucks

But for AA Fuel dragsters, they will use ammonia or some fluid to raise the tire temp with low dynamic friction so that the static friction improves. The same is true for Race Cars where the tire softness and friction loss temperature rise is optimized for the weather and lifetime of soft tires needing changes and lost racing time to change tires.

But generally, static friction reduces once any part of the tire loses contact at any speed or direction.
This is how ABS or automatic breaking system electronics works in cars. Once wheel slip is detected on braking, the brakes are pulsed-off to allow the wheels to turn, so the driver can steer. If the front tires are locked (dynamic friction) you cannot steer the vehicle.

p.s. we used to race British cars in winter of '69 on Ice andt he ones with front-wheel-drive and huge tungsten studs would go into hairpin corners at 60 MPH and then accelerate to pull the car around the corner.

once any part of the tire loses contact
I assume you mean loses static contact, i.e. starts to slip, not loses contact altogether.

TonyStewart