Question

when we try to push a very heavy box kept on ground,it does not move al all.which force is preventing this box to move forward?where does this force act?

Answer 1

when we try to move a heavy object the irregularities of the heavy box and the surface are locked so there is a friction which is static friction it is a self adjusting friction it balances the force applied but only upto a certain limit that is known as limiting friction but when the applied force exceeds the object moves..
This force act between a stationary object which has THE TENDENCY TO MOVE and the GROUND OR ROUGH SURFACE