Question

differentiate between reactive and active force

Answer 1

This has to do with how you define a system. How you choose to do this is basically arbitrary but certain ways are beneficial in certain circumstances. An internal force is inside the system and an external force is outside the system. That might sound pretty meaningless and in some ways it is entirely arbitrary. But there is something very important. Only External Forces can cause an acceleration. The classic example of this I like to give is that you cannot grab yourself by the hair and lift yourself up off the ground. That is because your hand is part of your body. So you cannot really create a system where your hand is external to the rest of your body. Of course you could define the system to be your body minus your hand and say your hand is external to this system. But when your hand pulls on your hair, your hair will pull back on the hand. And since your whole body is connected, ultimately, there will be no acceleration of the center of mass of the hand-body system. But somone else could grab you by the hair and pull you up off the ground. Another classic example of this is the idea of pushing a car. Can you push your car from the inside? No. That is because you are inside the system. You could push on the windshield, but the windshield will push back on you. But if you get outside of the car, you can push on the car with the aid of the friction/traction from the gound.

Active vs. Reactive
There is no difference. That is to say that there is no time delay. It's not like the action is first and then followed by the reaction. True Forces only can occur in pairs like this. One thing pushes on another and the other pushes back on the first. They both start and stop at the same time. The only difference between each is the opposite directions. It does not matter which you call the action and which you call the reaction. We have a habit of referring to forces exerted by a person as the action but that is truly arbitrary. For example, if you push on a wall, we tend to say that you pushing on the wall is the action and the wall pushing on you is the reaction. This is because the wall won't just decide to push on you. But you could define it the other way and there would be no loss of meaning. In order for the wall to push on you, you must push on the wall. In order for you to push on the wall, the