In diagram 1,F pulls the body. The molecule in contact with F gives an equal normal reaction opposite to F,the same happens with each molecule,how does the body move then?
In diagram 2, is the logic correct that 10 cm part is pulled by 24N so every molecule in contact will be pulled by 24 N that’s why it applies force of 24N on 20cm part?
The molecule in contact with F gives an equal normal reaction opposite to F
The first atom is pushed with F and exerts an equal normal force n back on the hand that pushes. This n does not act on the atom itself, but on the hand that pushes. So if the atom was alone, it would move since only one force pushes on it according to Newtons 2nd law: $$F=ma$$
But that molecule is not alone. It's motion is prevented by the neighbour atom. This second atom pushes back on the first with an equal normal force n. This n works on the first atom only. So now the first atom is pushed with F from one side and n from the other, and it should stop accelerating: $$F-n=0$$
This propagates from atom to atom through the object. Every atom thus ends up with balanced forces except for the very last one.
But the very last one with unbalanced forces makes the whole difference. Because now that last one starts to move. And as it moves, the normal force n that it exerts on the second-last atom decreases. That allows this second-last atom to move as well, since the forces on it do not balance out any more. This propagates all the way to the first atom, and they all start moving.
In this way the object as a whole is moving and accelerating in spite of internal forces cancelling out.
In fact the Newton mechanics are to simple to explain the small movement between molecules.Quantam mechanics is then developed.
