Consider a ball rolling without slipping on a horizontal surface. Obviously it is going to stop at some point, but why? Since the surface of the ball that is in contact with the surface of the floor has no relative motion to the floor, there can't be a force slowing it down there. So where does the slowing force come from?
1
-
$\begingroup$ Perhaps you can see it as a "succession" of events with static friction. Just an idea. Friction is somehow a "dirty" scenario, forces between the ball and the floor must be broken for the contact point to be lift and renewed. $\endgroup$– AlchimistaCommented May 12, 2021 at 13:03
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
There are forces other than a single-point (normal) contact force and the static friction: air resistance, surface or ball stickiness, multi-point contact, surface or ball flexing.
Consider the following comparisons: With an extremely hard/stiff surface and a perfectly round and hard/stiff ball, the ball will roll farther than a squishy ball. Or a ball on a flexible surface. Or a ball on a sticky surface.
In each of the shorter cases, the ball interaction with the surface is more than a single-point, purely vertical-point-contact-plus-static-friction interaction. There are forces other than contact (normal). Stickiness produces forces which cause torques opposing the rolling. If the ball or surface can deform (even slightly) kinetic energy is lost due to flexing and temperature increase.
A round steel ball on a clean flat steel plate will roll for a very long distance. If it could, it would roll until air resistance makes it stop.
$\begingroup$
$\endgroup$
2
First: there is friction -- we typically distinguish between "static" friction when two surfaces are sliding against each other, and "rolling" friction, which is a much smaller effect. <-- but not zero, so there is energy loss as the ball rolls.
The forces which slow the ball down are both rolling friction and air resistance in your case.
Now, I will note that a theoretical situation with perfectly frictionless surfaces could occur, if you were able to impart exactly the right amount of spin to the ball before launching it along the surface. It would appear to be rolling with no "sliding", but that would be coincidental.
answered May 12, 2021 at 13:31
-
$\begingroup$ What is the interaction which you classify as "rolling friction?" $\endgroup$– Bill NCommented May 12, 2021 at 13:57
-
$\begingroup$ @BillN "Back in my day...." :-) it was the force required for the two surfaces (ground, ball) to "peel" apart as the contact point changes. $\endgroup$ Commented May 12, 2021 at 14:46