There is an arm at the left side of the bottom roller. This arm can be bent or broken (like mine). Either get a new arm if needed or go to a dismantler and buy a used one and replace it. It is held in place with a single bolt (12mm I think).
i would say sliding
what stops food from sliding up from your stomach when your standing your head
coefficient kinetic
Friction.
Keel
sliding
The force that keeps a box from sliding down an angled conveyor belt that slopes upward is the friction
yes
traction
Friction
static friction
end caps and stops