0
$\begingroup$

I'm confused on a scenario. If we roll a ball on a horizontal surface and it rolls without slipping it should eventually stop due to friction. However rolling without slipping means the velocity at the point of contact is always 0. Since kinetic friction always opposes movement and the point of contact has v=0 there's no kinetic friction and static friction only arises when there is some force. Thus there is no friction? Can anyone clarify what is happening, and point to where I'm confused.

$\endgroup$

marked as duplicate by Qmechanic Jun 9 '18 at 16:06

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 4
    $\begingroup$ Rolling friction and air resistance would oppose the motion. $\endgroup$ – Farcher Jun 8 '18 at 11:53
1
$\begingroup$

As you are aware, both kinetic friction and static friction are zero when an object rolls with constant velocity. If these were the only forces available the ball will never stop rolling on a perfectly flat surface.

However, there are other sources of "friction". There is air resistance, and also rolling resistance. Rolling resistance is related to the fact that the ball and the plane are not perfectly rigid, they deform a little so that the ball is always climbing over a small hump, causing a small resultant force which opposes motion.

$\endgroup$
0
$\begingroup$

In reality there is no single point of contact but a small but finite area of contact and the velocity of all those points of contact is not equal to zero. So in realtiy there is no such thing as rolling without slipping. But I guess you are right that theoretically a ball with an area of contact --> 0 would not experience any loss of energy.

$\endgroup$
  • $\begingroup$ For a perfectly ridgid ball rolling on a perfectly rigid surface, yes. In reality, both the ball and the surface will experience stress at the point of contact and, because nothing is perfectly rigid, they both will experience strain. Also, in reality, neither the ball nor the surface is perfectly elastic, so at least some of the energy associated with that strain will be dissipated as heat. $\endgroup$ – Solomon Slow Jun 8 '18 at 13:56
  • $\begingroup$ P.S., If you don't perform the experiment in vacuum, then there will also be energy lost as the ball stirs up the air that it passes through. $\endgroup$ – Solomon Slow Jun 8 '18 at 18:07

Not the answer you're looking for? Browse other questions tagged or ask your own question.