An object moving in a circular path as observed from the ground frame is moving with some constant velocity along a non-smooth surface, my question is we know that Static Friction provides for the centripetal force for the body, but why doesn't the kinetic friction act since the body is moving with some velocity?

I appreciate all answers


If there is kinetic friction it will act tangential to the circular path, not perpendicular to it. So if you are wanting to analyze the centripetal component of the net force kinetic friction will not contribute to it.

If you want uniform circular motion with kinetic friction then you will need some other tangential force to counteract the kinetic friction force so that the tangential component of the net force is zero.

  • $\begingroup$ Thanks for the answer, but my question was that since the object is moving with some constant speed whose direction is always along the tangent to the point in the circle, why doesn't kinetic friction act along the tangent to slow down the speed of the object. $\endgroup$ – Archit Chhajed Oct 11 '20 at 12:30
  • $\begingroup$ In the presence of friction the particle will not move at constant speed -- unless someone is pushing it. $\endgroup$ – mike stone Oct 11 '20 at 12:33
  • $\begingroup$ I am asking this question since there exist scenarios where a car can take a circular turn with constant speed in various high school level physics problems where we can calculate a particular range of speed at which a particle moving along a rough surface can take a turn, but would not kinetic friction try to slow down the speed only? $\endgroup$ – Archit Chhajed Oct 11 '20 at 12:41
  • $\begingroup$ For example for a small interval of time, if we consider the motion of the object, it would be tangential and then kinetic friction for that particular instant would act along the tangent to slow down the object and since the magnitude of the kinetic friction would be constant the object would slow down informly and the direction of net acceleration would not be along the radial direction, $\endgroup$ – Archit Chhajed Oct 11 '20 at 12:44
  • 2
    $\begingroup$ @Ankit Thanks I think I now understood all the answers. All the scenarios of problems of constant speed in a circular path assume that there is enough Force at any instant in a direction opposite and equal in magnitude to that of the Force of Kinetic Friction, so Net Force along the tangent would be zero, hence maintaining constant speed. $\endgroup$ – Archit Chhajed Oct 11 '20 at 12:52

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