What interaction generate the mechanical force? It is said that there are four interactions which govern various phenomena of nature. Then when force applied on a body - what interaction really generate this force and make the body to move? Can we replace Newtons laws and expressions of mechanics in terms of interaction responsible? 
 A: Most mechanical forces - for example, when you push on a door and it swings open, or you pull on a rope to lift a box tied to the end - are the result of electromagnetic forces. When one object pushes against another, the electrons at the surfaces of the two objects repel each other and push away, which is why your hand doesn't pass through the door. On the other hand the attractions between atoms within each object, again involving electrons and now protons as well, are what hold the object together, so when you pull on a rope it doesn't immediately come apart in your hand.
Other mechanical forces such as air resistance and friction also arise from electromagnetic forces. Air resistance comes from molecules/atoms in an object repelling molecules/atoms in the air and being repelled the opposite way in return; friction comes from the atoms in two sliding surfaces bumping across each other and converting their linear kinetic energy into heat (atomic vibrational energy).
Gravity is only relevant to mechanics in that it causes small accelerations in free-falling bodies, and the strong and weak nuclear forces are only applicable inside the compound subatomic particles, so none of those have any direct application in mechanics. Electromagnetism dominates the small scale of that discipline.
