But then what does inertia mean at all!? Cant we calculate how much it resists the applied force? I mean considering an imaginary plane with no friction but gravity as of Earth and an enormous mass of square shape is standing on the plane at equilibrium(say rest) like a 1000kg. So if we have to make it start moving what force should be applied to make it move? or is it any force no matter how small will set it into motion with a corresponding final velocity? and another doubt is force itself.. if we are pushing against a wall for example.. what would be the force applied? in the eqn F=ma what would be the mass and acceleration taken as? and will it be of the body applying force (us) or will it be the body receiving force(wall)? I have really confused myself today. Sorry if its really silly. I just wish to understand it clear and complete. Thank You.
Inertia is the term we use to say that an object can't change its velocity without a force acting on it. This does mean that a force always changes the velocity of an object (if net force is not zero). The wall scenario is a bit different because the wall will feel the force and will try to change its motion accordingly but in this case, inertia has less to do with the fact that the wall barely moves. Here there are simply other forces like the connection between ground and wall that balance your push sufficiently to keep the wall stable.