Hi, I'm a new member here! I don't like introductory by questions, but I think this is the best place to do it. My questions concern the normal force, Something that seems intuitive at first, but the details a little unclear. 1. The problem statement, all variables and given/known data I'll break down my questions into parts: 1) I'm taught in my high school syllabus that a weighing scale (weight) measures the normal force on an object. My first question concerns on how exactly is it really measured? Of course, the normal force is essentially... a force. Therefore, I infer that the scale utilizes some "springy" mechanism, and some kind of system measuring how much it is "resisting" the force on it. Is this so? If it is, then on to my second question.. 2) I wanna illustrate this with a classic textbook example: measuring the "apparent weight" of an object A on an accelerating elevator using a weighing scale.Now let the elevator be accelerating upwards. I am taught that the Normal force (read from scale) = mg + ma (I think this formula accounts only for the magnitude [or converts the mg downwards to it's third law pair), thus no need for negative values). So my 2nd question is how exactly does the scale measure this? I can't see a way how my hypothesis for the 1st question explains this: I can't see how the spring "resists" the force upwards while adding up to the normal force that way. The whole scale accelerates upwards, and I don't see some parts of the spring accelerates more than the other parts of the spring. I'm probably mistaken something here. 3)Now, take the normal force, mg + ma. Newton's third law of motion asserts that there is an opposing force exerted by the object on the scale in the direction of gravity. My question for this part is this: How is this possible when the object is accelerating upwards? Where did the additional force ma come from? I pose a similar question when the elevator is accelerating downwards. The scale reads mg - ma. But if the body (and everything) is accelerating downwards, why is the force on the scale reduced by ma? Clearly, I am misunderstanding something. What is wrong with my argument? I think I get it if I see it in a free body diagram of the situation, when the vectors superposes and adds up, but I'm missing something in the details in how the "flow" of the force works. A "chronology" of the happenings will help here, I think, like the accelerating elevator will cause A to happen and then A will cause B to happen. I think essentially, my problem lies on how and why the vectors (counter gravitational pull force + the force accelerating the body) adds up. Or is it just a "detached happening" just on the scale? 4) Suppose an object A is at rest on a flat weighing scale on earth. Newton's third law of motion asserts that there is an opposing force of gravity which is equal in magnitude but opposite in direction. So Normal force = mg. Now suppose the object A is free-falling and strikes the same flat weighing scale. According to Prof. Julius Miller in his program, the scale reads twice the weight of the object during contact. In this situation, it seems that the Normal = mg (gravitational pull) + ma (the push on the scale? the net force? Or is it contact force? Not so sure here too.). How exactly does the vector add up? Should the vectors of different "type" of force superpose like that or am I misunderstanding what Prof. Miller is trying to explain? I am aware that the gravitational pull and the normal force are not third law pairs, but I think the problem I'm having is with the understanding of the normal force's counter pair (contact force?). I hope I stated my question clearly. Thanks in advance!