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