Fa represents the applied force (let's say...by a rope)
Fg represents gravity/weight of the object
Ff represents friciton, i.e. the small amount of air resistance
But here's my question.
By Newton's 3rd law of motion if a force is exerted on an object then the object will exert a force which is equal in magnitude and opposite in direction. Essentially, all forces act in pairs.
Still assuming that the object is attached to a rope and is being pulled up by it, then the rope is clearly exerting a force on the rock (causing it to accelerate upwards). But what is the reaction force to this? Is there a force being exterted on the rope by the rock but it's insignificant and thus not included in the diagram?
If anybody could clear up this element of confusion of mine I'd be really grateful!
Thanks in advance.