Hamster in Cage: Internal or External Forces?

[cepheid]

I remember seeing a commercial advertisement in which a hamster in a cage moved itself towards a desirable item (food or something) that its owner had on the counter by throwing itself against the side of its own cage. Would this really be possible? On the one hand it seems like there are only internal forces within a hamster/cage system. On the other hand, I can't think of why it wouldn't work. The hamster just needs to apply enough force to the side of the cage to overcome static friction between the countertop and the bottom of the cage.

 

[mgb_phys]

It works because the friction is slightly different for slow forces and fast changing forces.
It's the same principle as getting yourself spinning on an office chair.

In an ideal world the hamster running across the floor would move the cage backward as much as hitting the wallmoves it forward - in the real world the slow forward motion doesn't break the static friction, but the rapid accelearation of hamster+wall does.

 

[cepheid]

Ohh...that's so simple once explained, but I couldn't seem to work it out.

 

[icelevistus]

To get mystical, the friction results in the system not being isolated. You end up having to consider the whole world(!)