If suppose I keep an object on a table. The forces will be the weight of then body and the normal reaction from the table. Will there be any other forces? There is air present everywhere and it also applies a force = pressure x area. Can we include that too? (I know it will cancel out but then also...)

Question

anonymous · Answer

need not .. for newtonian physics.. we usually do not include the air pressure, unless exclusively mentioned, thats why the velocity and acceleration of the objects do not depend on the MASS, but in reality it depends cause of air resistance, newtons laws of motion do not consider air resistance, hence no force due to air, and no pressure due to air

unicorn · Answer

as said above velocity and acceleration of the objects do not depend on the MASS does that mean you are saying force is not equal to mass times acccl of body

anonymous · Answer

what I am saying is, when you apply force , there is frictional force from the air in the opposite direction we do not consider that,  

and motion in uniform velocity is govern by 3 sets of equations (newtons) again which do not consider mass!

P.S. Force applied does not depend on mass, but the acceleration gained by the mass depends on it!

panther · Answer

btw, we don't consider air pressure because the force on the object is the same from all directions because the air pressure is for all pragmatic purposes equal everywhere around the object.  Hence all of the force from air pressure cancels.

anonymous · Answer

@panther, not if the box is kept on the table, then there IS a net AIR pressure acting on the box!.. air pressure cancels out, only if somehow the box is floating in the mid air, even when its moving in air, there is a net air pressure cause of the movement!