A heavy weight is resting on a surface with, with the normal force equal to the weight. So the object is stationary. (W = N)
Now I try to lift the heavy object so I'm exerting some upward force U. The object is still stationary, so it must be the case that W = N + U. And that means that the normal force has decreased.
Question: How does the normal force know how much to decrease?
Trying to clarify the question:
It's clear to me that Fnet = 0. My question is how does it stay 0? How does the normal force "know" how much it needs to decrease to keep it at 0?