Hi experts .pls read the following question and answer my query in accordance to newton 3rd law i.e action= reaction Q- if exert a force on wall to push it ,the wall exerts the same magnitude of reaction force on us ( acc. To newton 3rd law) ..*then why dosen't the wall move* ? If the wall doesnt move by cancel out of forces ..how does the table move if we apply a force on it ,as table would have also applied the same force on us ;then why in table case forces do not cancel each other* ... Also then why rocket moves up- *why in rocket case action and reaction do not cancel each other* .? .. (experts pls ans my questions highlighted in *asterisks)
Dear Student,
Newton's third law of motion says that for every action there is an equal and opposite reaction.
When you exert force on a wall the wall exerts an equal force on you. But there are two systems involved in it: you and the wall. So these two forces never cancel each other.
When you are considered as the system, forces acting on you are considered and not by you. So, the force exerted on you by the wall will be taken into account for explaining whether you will move or not. You don't move because you push your legs against the ground in exerting force on the wall. So the ground exerts an equal but opposite force on you what the wall have applied on you. Both these forces thus cancel and you do not move.
The same happens with the wall because your force is not stronger than the static friction of the wall relative to the ground.
Answer to you 2nd query:
When you apply force on a table it moves because if you take table as the system, the force acting on it will e considered and not by it. The table moves because your force is greater than the static friction between table and the ground. If you are not moving due to the same reaction force acting on you by the table, then some other forces are also acting on you like, the static friction between your feet and ground and the force of the ground as a reaction of the force with which you push the ground. These forces cancel each other and you don't move.
Answer to your third query:
Rockets move upward by expelling gas backward at high velocity. Doing so it exerts a large backward force on the gas in the rocket combustion chamber, and the gas therefore exerts a large reaction force moving the rocket upward. This reaction force is called thrust.
Regards
Newton's third law of motion says that for every action there is an equal and opposite reaction.
When you exert force on a wall the wall exerts an equal force on you. But there are two systems involved in it: you and the wall. So these two forces never cancel each other.
When you are considered as the system, forces acting on you are considered and not by you. So, the force exerted on you by the wall will be taken into account for explaining whether you will move or not. You don't move because you push your legs against the ground in exerting force on the wall. So the ground exerts an equal but opposite force on you what the wall have applied on you. Both these forces thus cancel and you do not move.
The same happens with the wall because your force is not stronger than the static friction of the wall relative to the ground.
Answer to you 2nd query:
When you apply force on a table it moves because if you take table as the system, the force acting on it will e considered and not by it. The table moves because your force is greater than the static friction between table and the ground. If you are not moving due to the same reaction force acting on you by the table, then some other forces are also acting on you like, the static friction between your feet and ground and the force of the ground as a reaction of the force with which you push the ground. These forces cancel each other and you don't move.
Answer to your third query:
Rockets move upward by expelling gas backward at high velocity. Doing so it exerts a large backward force on the gas in the rocket combustion chamber, and the gas therefore exerts a large reaction force moving the rocket upward. This reaction force is called thrust.
Regards