what is the direction of friction when a cylinder rolls up an inclined plane?

Question

does it depends on the fact,whether the cylinder moves up or down? please give some explanation too

Answer 1

So far both answers are wrong! The friction is not related to the motion of the entire cylinder, it is only related to the location where the cylinder meets the slope. Assuming that the cylinder is rolling freely (not being driven), the friction is what causes the cylinder to spin.

Friction is only opposite the movement in cases of dynamic (kinetic) friction. I believe this question assumes that the surfaces of the slope and cylinders are not sliding in respect to one another, therefore this is static friction. (Otherwise, no movement would mean no friction)


The friction will be in the opposite direction to the motion of the cylinder at the point of contact. Since the cylinder is moving up the slope, the bottom of the cylinder is actually moving rearward in respect to that motion. Therefor the fiction is also in the rearward direction to cause the cylinder to spin.

If the cylinder was being driven (turned) to cause it to climb the slope the case is different. In this case the friction is forward or up the slope.

In the answer below, the writer discusses the balancing of fricitonal forces. This is correct. The frictional forces I am mentioning are those acting on the cylindar. An opposite force is being applied by the cylindar to the slope.

Answer 2

If the cylinder is under power, such as a car going up or down, if there were no friction (icy road), then in both cases it will slide down. Therefore the direction of friction in both cases is uphill.

If the cylinder is falling freely, if there were no friction, it would not roll. Therefore the direction of friction is uphill, causing it to roll in the direction of its descent.

If the cylinder is ascending because of its own momentum, if there were no friction, it would not roll. Therefore the direction of the friction is downhill, causing it to roll in the direction of its ascent.

Finally, if the cylinder is descending faster than freefall because it's under power, the direction of friction is downhill, unlike as in the first example, in order to go faster than freefall.

So, it does all depends. You do a force analysis at the point of contact with the road, which will be a combination of wheel torque and gravitational acceleration, in order to determine the direction of the friction.

Answer 3

Part I (obvious)
The cylinder will roll _down the hill with smaller acceleration,
than sliding block. Because part of its potentialy energy
has to go into rotational acceleration. The force slowing
rolling cylinder with respect to sliding block is the force
of friction, acting on the cylinder in _uphill direction.
In absence of friction the cylinder cannot roll, it will skid.

Part II (obvious too)
Accleration of rolling cylinder is the same regardless
of whether it rolls _uphill or _downhill. Just as acceleration of
a cannon ball is the same g downwards, regardless whether
the cannon ball is on acsending or decending portion
of its trajectory.

Part III (even more obvious)
Since acceleration of _uphill motion is the same as
acceleration of _downhill motion, the forces which
cause acceleration mentioned thereabove are
also the same.

Conclusion (should be obvious now):
The force of friction acting on rolling cylinder is always
directed _uphill, regrdless of direction of cylinder motion
(uphill or downhill).

Answer 4

DT is correct, but there are always 2 equal and opposite friction forces, one on each surface. So you have to specify the surface that friction is acting on.
If the cylinder is not being driven, there is a downward force on the cylinder causing it to spin, but an equal upward force on the surface of the plane.
For the driven cylinder, there is an upward force on the cylinder causing it to move up, and a downward force on the plane.

Answer 5

Friction by definition is a force that opposes motion. Therefore if the cylinder is rolling up the inclined place then friction is going down.
If the cylinder was rolling down then friction would be going up.

Answer 6

In case of rolling there is an extra friction besides the sliding, acting as a momentum against the rolling. Therefore the resultant friction its not quite along the slope...There are necessary more details for exact analysis.