4
$\begingroup$

When a cylinder performs pure rolling while on an inclined plane,

enter image description here

Why does friction act on the bottom point?

In pure rolling the bottom most point is at rest, so there is no sliding over there. So why does friction come in the picture?

$\endgroup$
4
$\begingroup$

The essence of static friction is that it acts to prevent motion even in the presence of some outside force.

The desk I'm sitting at while I type this is homemade and thus almost certainly not perfectly level. Yet the items on the desk are all fixed in place, not sliding down the slight slope. (OK, pencils tend to migrate by rolling, but..). It's the force of static friction that keeps stuff where I put it, despite the component of gravity parallel to the desk's surface...

$\endgroup$
  • $\begingroup$ True. Kinetic friction acts when there is sliding. Thanks. $\endgroup$ – Slav Apr 29 '15 at 10:37
1
$\begingroup$

All the other forces except friction acting on the ball have their line of action pass through the center of mass. So, friction is the only force which can provide torque in the above example. Therefore, in order for the ball to roll, you need friction.

$\endgroup$
  • 1
    $\begingroup$ As there is no sliding, there should be no friction in the first case. $\endgroup$ – Slav Apr 28 '15 at 17:37
  • 1
    $\begingroup$ But if there is no friction, than the ball will just slide down the ramp, not roll. Friction is needed for it to roll as @Goobs said. $\endgroup$ – Jon Custer Apr 28 '15 at 17:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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