Final answer:
Gravity acts equally on all blocks regardless of their position in a stationary elevator. Friction, on the other hand, applies a force in the opposite direction to the motion of a block sliding across a floor.
Step-by-step explanation:
The force of gravity acts equally on all objects regardless of their positions relative to each other, provided they are in the same gravitational field and not undergoing acceleration (ignoring any negligible differences due to altitude in the stacked blocks). Therefore, in the case of a stationary elevator with 3 blocks stacked on top of each other, gravity will act the same on the top block, the middle block, and the bottom block. When considering friction, however, which is a different force, it opposes the motion of moving objects. For a block being pushed across a floor, the force of friction would be in the opposite direction to the block's motion, directly counteracting the molecular interactions that occur between the block and the floor surface.