Force – An action? Or a reaction?
Have you ever fallen hard on the floor? I’m sure you have. Ever wondered why the floor is not banged up like you are? According to Newton’s third law, for every action force there is an equal and opposite reaction force. So, you must have caused the same amount of damage to the floor that you have experienced, right? We’ll find the answer to that question soon. Before that, let’s slow down for a minute and look at what exactly happens when you fall on the floor.
You have exerted force on the floor when you fell. The floor has also exerted the same amount of force, but in the opposite direction, i.e. on you. You see a bleeding wound on your knee. But, there is no proof on the floor of your falling.
What do you think happened to the force exerted by you? Did it get cancelled out with the force exerted by the floor on you? No. The force exerted by you is on the floor and the force exerted by the floor is on you. You and the floor are two different systems. Thus, the forces do not get cancelled out.
Is the force exerted by the floor greater than the force exerted by you? No. The action and reaction forces are of equal magnitude.
Hmm….. What could have happened then? Let us see how familiar you are with Newton’s second law.
The acceleration of an object is directly proportional to the unbalanced force applied and in the direction of force. To break it down, acceleration can occur only when the net force on an object is not zero. In our scenario, since the forces are acting on two different systems (floor and you) the net forces on both the systems are not zero.
This is starting to become a problem now. Where did the force exerted by you on the floor go? Before you get riled up. Have you thought about the masses? Force is directly proportional to the mass of the object. The mathematical equation of Newton’s second law of motion, F = ma will answer our question. Acceleration is inversely dependent on mass, i.e. the heavier an object is, the greater force you have to apply to accelerate it. Let me try and make it more simple for you. The forces are equal, the masses are unequal; hence, the accelerations are unequal.
As you know, the floor is attached to the building, which is attached to the Earth. Earth as a whole is so much greater than you in mass. This is the reason the effect of the force exerted by you isn’t visible on a large scale. In other words, you can see no visible accelerations on the floor’s part.
This is why some objects bounce while others don’t move even an inch. Some common examples for you to analyse are – a runner running on a road. The runner applies force on the ground and pushes backward. The ground in turn pushes the runner forward. A person sitting on a chair is applying downward force on the chair. The chair in turn is applying upward force on the person and holding him in place. The basic point we need to understand is that a single force cannot exist. Forces are always an interaction between an action and its reaction.
– Beena P V