Three blocks are being pushed by the force $F$. The horizontal surface and surface between blocks 1 and 2 are smooth. Only the surface between blocks 2 and 3 is rough. We did not consider the normal force between $m_1$ and $m_2$, as my teacher said that we should only consider the normal between the required surfaces.
Here, we have two blocks on top of each other, so according to his logic, to find friction between ground and block, we should not consider the force of upper block on the lower block as it is not in direct contact, but I think that should not be the case.
Please explain the concept as I am very confused.