Boundary drag on the wheel as it spins causes a loss of angular momentum, and so it slows over time unless force is applied (via adorable hedgehog legs) to keep it constant. Additionally, there are likely normal frictional forces at the meeting of the wheel and the supports, as I highly doubt they gave the pet a wheel with magnetic bearings in a vacuum.
And yes, the hedgehog must exert constant force in order to overcome this viscous friction.
On a related note, this viscous damping term scales as velocity, so the faster the wheel turns the harder the little thing has to work to keep it at a constant velocity.
And yes, the hedgehog must exert constant force in order to overcome this viscous friction.
On a related note, this viscous damping term scales as velocity, so the faster the wheel turns the harder the little thing has to work to keep it at a constant velocity.