Consider a wheel of mass `M` and radius `R` up against a ledge of height `h` , where `hltR` . What horizontal force `F` do you have to apply to the axle to roll the wheel up over the ledge?
The wheel will roll up if the torque due to the horizontal force `(tau_F)` exceeds the torque due to the force of gravity `(tau_g)` .
This is the solution. Notice if `h->R` Then `F ->oo` . If `h->0` ,` F->0` . This is intuitively reasonable.