1. The problem statement, all variables and given/known data A uniform plate of mass M stays horizontally and symmetrically on two wheels rotating in opposite directions. The separation between the wheels is L. The friction coefficient between each wheel and the plate is N. Find the time period of oscillation of the plate if it is slightly displayed along its length and released. http://[PLAIN]http://i61.tinypic.com/25thrlw.png [Broken] 2. Relevant equations My teacher solved this problem in class and i understood everything except the direction of friction. The plate moved to right by distance x. http://[PLAIN]http://i61.tinypic.com/ixwpci.png [Broken] 3. The attempt at a solution According to me right wheel should have direction of friction inside. Because plate wants to move out. So it will try to move back the plate left side.