This isn't really a single question, but rather a series of speculations, where you can hopefully help me understand some of the things. Soo.. Classical mechanics are, at least on basic level, based on the euclidean geometry, which allows you to add forces as vectors. Often this means that we can solve a problem that involves forces by inserting a proper coordinate frame and breaking the forces into their horizontal and vertical components. Now, this is something that I have more or less accepted to be a truth in nature, although I do know that in relavistic mechanics space is not euclidean, but let's forget about that for now. What I want to ask about, is some of the consequences of force superposition that always makes me speculate and that I never have a proper answer to. On the picture attached, I have drawn a pendulum bob connected to the wall by a string. In class one learns how to break the weight of the pendulum into a force that pull along the string, and into a force that pulls perpendicular to the string. By doing so you can show that the force is approximately proportional to the amplitude for small angles etc. I just want to ask why you know that this is the correct way to break down the force. How does the weight of the pendulum "know" that it must pull along the string? For me this can't just be a consequence of the postulate that space is euclidean. Can someone explain what happens on microscopic level that supports, that you actually can break the force into those components and not just any two components?