Question

suppose object a pushes b and b falls down why not a falls down according to newton's third law

Answer 1

here we get a rxn force but it's weak and friction force to helps

Answer 2

Newton's Third law is
For every action, there is an equal and opposite reaction.

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object.

say you push your finger against a window
look closely at your finger you can see the force exerted back on your finger skin is moved causing discoloration.
for me being a pinkish color turns yellow you may see a different reaction. T
he force you apply to the window is dispersed across the surface and you can see it bend maybe even hear it shift. If you push hard enough you could break your finger or break the window.

you pushing on the window exerts force onto the window the window resists the force pushing back on your finger. hence equal and opposite reaction.

if you want to get really technical the atoms that make up your skin never actually touch the window there is a barrier of electrons that however small the decimal of the distance the atoms of your body never actually touches the atoms of the window.