Theoretically (I thought) static friction does no work. Practically, this answer says it does and it's using a conveyor belt as an example.
My question here is: In the conveyor belt case, are the groceries moved by the friction force? Or by the belt, and the static friction is just a way of interlocking the groceries onto the belt.
To emphasize my point l, I'd like to use an example of two lego pieces made of some frictionless material stacked up on top of each other, interlocked by their shape and the gravity. If we move the bottom piece and it in turn moves the upper piece, would it be correct to say that the shape or the interlocking system moved the upper piece? Or can we simply state that the bottom piece moved the upper piece and by doing so sticking to the idea that static friction does no work (?)
We can go even further with the shape vs friction. We can take a cubical block of frictionless material and a U-shaped piece of same material. The U-shaped piece pushes the cube on a table slightly upwards. Can we still say that the way the two interlock and are able to move each other is somehow called friction?
Or a spoon pushing a small ball upward?
I mean at what point do we start saying that the one object pushed the other instead of "the friction" ?