Question

Specify two differences between internal and external forces

Answer 1

Internal forces are the forces that emanate from within a system. The system must be defined by you/problem. 

External forces are the forces that emanate from outside the system. 

An example: Let us say, our system is earth-sun system. You see, we have defined the system first. Now, the force of earth on sun, and the force of sun on earth ( Mutual forces of gravitation, say ) are the internal forces. 

But, the force of Mars on sun or on earth, would be called external force here as it is emanating from outside the system that we have defined. 

Regarding, active and reactive forces: If you mean action-reaction pair, here is the answer: 

Action or reaction force has no difference. Whenever two bodies or two systems interact, they exert force on each other. Any one of these forces could be called action force, and the other as reaction force. So, if you kick the ball, the action could be the force by the ball on your legs, and the force by the leg on the ball could be reaction force. 

Also, there is no time lag between the action -reaction pair, i.e., they happen at the same instant. Therefore , none is earlier or later- they both come into existence simultaneously.

hope it helps):-

Answer 2

❁ΔŇŞŴ€Ř❁

◆ Internal forces of the earth:

1. Act from within the earth towards the surface.
2. Eg. Volcanic eruptions and earthquakes.

◆ External forces of the earth:

1. Act on the surface of the earth.
2. Eg. Moving ice, water, etc.