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Forces induced by a vehicle wheel on the ground

  1. Sep 9, 2015 #1
    Hi, I was wondering whether anyone can help with a question I have about the forces acting on a car wheel and the forces the wheel induces on the ground surface.

    The way I understand it, a car wheel traveling on a flat surface has the following forces acting on it:
    -vertical force due to the weight of the car (acts at centre?)
    -a torque applied by the engine at the axle
    -a horizontal force in the direction of travel (is this separate to the torque or just a component of it?)

    I was not sure how these forces acting on the wheel can be translated to forces at the ground-wheel interface. I know there will be a horizontal force in the opposite direction of travel, and a possibly eccentric vertical force acting on the ground. Is there also a torque? Or is this completely incorrect? I have included an image of what my understanding is. Any help would be greatly appreciated.
  2. jcsd
  3. Sep 9, 2015 #2


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  4. Sep 11, 2015 #3


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    You got it right. The torque applied to the wheel from the engine gets transferred to the perimeter of the wheel as a force pushing the road back (via friction between the tire and the road surface). The reaction force from the ground (Newton's third law) pushes the car forward.The weight of the car creates a vertical downward force. The car is supported by the reaction force of the road surface.
  5. Sep 11, 2015 #4


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    Forget all the stuff above the ground and simply look at the ground plane. For a two dimensional contact patch, there can be at most three forces. (1) a force normal to the ground, (2) a force in the direction of travel, and (3) a force perpendicular to the direction of travel. That's all.
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