text: hats off to the one who answers this mechanics question !!!!!!!? a sphere performs pure rolling upon an inclined plane with inclination "theeta " with the horizontal . what is the direction of frictional force  when it performs pure rolliing up the plane and then comes down the plane performing pure rolling this time too ???!!! assuming the sphere rolls and never slides, which would cause it to lose its translational as well as rotational kinetic energies, the direction of frictional force going up the plane is downward, while the direction of frictional force going down the plane is upward.  that is because the plane provides the sphere with the friction to travel in the opposite direction.