作用力和反作用力

You should know that there is a famous law in Physics, namely Newton's 3rd law.

For every action, there is a reaction. Also, the two forces should act on different objects and the magnitude of them should be equal. (Newton's 3rd law)

For example, when you push someone, the force you exerted to the one you push is an action.

But, you will move backward also, since the one you push will exert a force, namely reaction, to you.

There are acting on two different objects(you and the one you push) and their magnitudes are the same.

For instance, action(作用力), reaction(反作用力)