Car turning on an unbanked (level) surface

[Bipolarity]

I've been trying to understand this:
http://www.batesville.k12.in.us/physics/phynet/mechanics/circular motion/an_unbanked_turn.htm

What I can't understand is why the frictional force equals the centripetal force. As the car turns, the frictional force should be opposite (antiparallel) to its velocity, and thus normal to the centripetal force, since the centripetal force is normal to the velocity.

What am I missing here? All help is appreciated thanks!

BiP

 

[Nugatory]

I've been trying to understand this:
http://www.batesville.k12.in.us/physics/phynet/mechanics/circular motion/an_unbanked_turn.htm

What I can't understand is why the frictional force equals the centripetal force. As the car turns, the frictional force should be opposite (antiparallel) to its velocity, and thus normal to the centripetal force, since the centripetal force is normal to the velocity.

What am I missing here? All help is appreciated thanks!

BiP

The frictional force is acting between the road surface and the tire patch that is in contact with the road. That tire contact patch is (as long as the car is not sliding) at rest relative to the road, and no matter which direction you try to push it, the frictional force will resist. The car wants to go in a straight line, pulling the tire patch towards the outside of curve, and the frictional force between tire patch and road is resisting.

You might also want to read #21 in this thread. https://www.physicsforums.com/showthread.php?p=3984064&highlight=Tire#post3984064

 

[Bipolarity]

The frictional force is acting between the road surface and the tire patch that is in contact with the road. That tire contact patch is (as long as the car is not sliding) at rest relative to the road, and no matter which direction you try to push it, the frictional force will resist. The car wants to go in a straight line, pulling the tire patch towards the outside of curve, and the frictional force between tire patch and road is resisting.

If the frictional force is opposite the (tangential velocity), it should be normal to the centripetal acceleration. I don't understand why this is not so.

BiP

 

[Nugatory]

If the frictional force is opposite the (tangential velocity), it should be normal to the centripetal acceleration. I don't understand why this is not so.

BiP

It's not opposite to the tangential velocity, because there is no tangential (or radial) velocity to be opposite to - the bit of tire that is touching the road is momentarily stationary.

I edited my first response above to add a pointer to an older thread on this topic:
https://www.physicsforums.com/showthread.php?p=3984064&highlight=Tire#post3984064

 

[PJC01]

olarScientist: Thank you for reaching out for clarification on this topic. The concept of frictional force equaling the centripetal force on an unbanked surface can be a bit confusing, so let's break it down.

First, let's define what we mean by an unbanked surface. This refers to a surface that is flat, or level, and does not have any incline or banked angle. In this scenario, the only forces acting on the car are its weight (due to gravity) and the normal force from the ground pushing up on the car to support its weight.

Now, let's look at the forces involved when the car is turning on this unbanked surface. As you correctly pointed out, the frictional force is always opposite to the direction of motion, in this case, the direction of the car's velocity. This means that as the car turns, the frictional force will always be pointing towards the center of the circle that the car is following.

At the same time, the centripetal force is the force that is required to keep an object moving in a circular path. In this case, it is provided by the frictional force. This is because the frictional force is the only force acting on the car that is not balanced by another force. The normal force from the ground is balanced by the weight of the car, so it does not contribute to the centripetal force.

Therefore, the frictional force and the centripetal force are equal in magnitude and direction, as they are both pointing towards the center of the circle. This is why we say that the frictional force equals the centripetal force in this scenario.

I hope this helps to clarify the concept for you. Keep exploring and questioning, it's the foundation of scientific thinking!