Reaction force explanation? I heard that reaction force is the total force applied back due to electromagnetic repulsion between the atoms of the thing that exerted the force and the thing that the force was exerted on, so can anyone help me understand that. And if that's not true can anyone give me the right explanation.
 A: That's not a very general description of a reaction force.  The truth is, every single force is a reaction force!
Here's the basic idea behind Newton's 3rd law: 
Whenever two objects interact, they put an equal and opposite force on each other. There aren't any "lone" forces - they always come in equal and opposite pairs, because they always arise during interactions between two objects.
That's it - it isn't really any more complicated than that. All that hand waving about electromagnetic repulsion is completely besides the point.
If I push on your shoulder, then your shoulder necessarily pushes back on my hands at exactly the same time with exactly the same amount of force, and the exact same type of force, in exactly the opposite direction. The force your shoulder puts on my hand could be said to be a "reaction force" to the force my hand puts on your shoulder, or just as well you could say that the force my hand puts on your shoulder is the reaction force to the other one.
It doesn't have to be electromagnetic repulsion either, any old force will do. If the Earth puts a gravitational force on the Sun, the sun puts an equal and opposite gravitational force on the Earth.
