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I understand when a car turns, it requires centripetal force and this comes from static friction of the tires. But my question is how? How does friction as in the picture below push outward to the left?

Is it because as the car begins the turn the right, the car is continually thru the rear wheels and its inertia driven forward. The tires, acting like a ski in snow or inclined plane, but stuck to the ground with static friction, push the road forward and to the left?

Found this description and it felt like it made sense. Just trying to conceptually understand how the inward centripetal force is created when there is static friction during a turn.

enter image description here

Qmechanic
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Kevin C Speltz
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1 Answers1

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So you want to understand how the tire generates a force that is lateral to the vehicle direction.

You may want to take a look at cornering force. This force comes from the fact that :

  1. The tire has a contact area with the ground. Forces between tire and ground can be exchanged over this area.
  2. Tire is elastic and thus deformable. The lateral force comes from the deformation due to the difference between the vehicle direction and the tire orientation.

Let me explain this with a beautiful drawing. The friction is in opposite direction to the vehicle speed. If the tires are turned, they are deformed. They are elastic so they want to go back in their rest position. However, there is friction between the ground and the tire. This will cause a force on the ground, which I called here Elastic Force. This force is the source of the lateral force on the vehicle.

forces

I'm not sure you want to compare it to turning with skis. In the latter, the lateral force is caused by the fact that you're are bending on a side to turn.

Read about cornering force and I guess you will understand it easily :)

Setoh
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  • Yes, cornering force is the next step. But there still has to be a lateral force of friction on tires, which causes the tires stretch lateraly. So without going into cornering force, i am trying to just understand the friction forces at the tires/road itself – Kevin C Speltz Jul 06 '21 at 16:01
  • check the edited answer and let me know if it's clearer for you. – Setoh Jul 06 '21 at 17:09
  • i cannot see the force drawing you made. Can you correct it? Otherwise, i assume it is similar to the picture above where the stretch in the tire and lateral forces of friction are all pointing similar – Kevin C Speltz Jul 06 '21 at 18:26
  • do you see it there : https://i.stack.imgur.com/yZBo5.png ? Yeah, quite close to the other discussion. – Setoh Jul 06 '21 at 18:33
  • i see it now. I see what you mean. As we turn the tire, it does twist the contact patch and turn the wheel as a whole at an angle to the current vehicle velocity, This creates the perpendicular force on the ground, which causes the reaction force/centripetal force on the tire/car etc. We are saying the same, yours just looks more detailed in the deformable body of the tire – Kevin C Speltz Jul 06 '21 at 20:27
  • If you think about this with an old school wood wheel, where no deformation is possible in the contact area, you should now be convinced that we can't turn a vehicle with an undeformable wheel :) – Setoh Jul 06 '21 at 20:55
  • @Setoh how did a horse and buggy make a turn if their wooden wheels were undeformable? – john Jul 12 '22 at 13:45