Supply And Demand Curve Doesn't Make Sense Mathematically

Hello, YouTube! Today I'd like to speak in English These days I am reading a book on Economics in Japanese This book here But I am reading this book, but I am not liking it much. I am not sure if this book is wrong or if the Theory of Economics itself is wrong. One of the things I don't agree is the Supply and Demand Curve. Usually they show you a graph with 2 curves and they say there is a point of "equilibrium" in this graph when the 2 curves cross each other. And this is one of the ideas I simply don't understand My feeling is that this kind of idea doesn't make sense mathematically Mathematically speaking that kind of drawing, that kind of graph doesn't make sense. These days I have been thinking about it and trying to understand I am not sure if I am wrong or if the books on Economics are wrong I think these books on Economics are wrong. First of all: what is supply? What is demand? Exactly? Is it a quantifiable number? Is it a number that can be measured? Is it a number that can be measured from the real world? Apparently as I am reading this book, supply is defined as just a curve on the graph. When you say that supply increases, you are saying that the curve shifs either left (or right, I don't know) And demand is also the same thing The definitions of supply and demand are very vague, at least in this book. When they say that demand is increasing, the demand curve either shifts right or left on the graph. Mathematically speaking it doesn't make sense, actually. I was trying to redefine supply and demand and make them measurable numbers. Just like in Physics. In Physics everytime you have some kind of quantity, these quantities are measurable, that is the usual way in Physics. I am starting to think that economists don't know Mathematics or Physics. It would be a good thing for economists to learn more Mathematics and Physics and try to imitate or follow those models. Because Physics is probably the most advanced of all fields in Science. And Economics is so vague I have this book, it is filled with graphs, but these graphs have no meaning mathematically. That is one of the things I just can't understand. I am trying to find to understand or maybe redefine these things. Is it necessary to know Economics to be a good investor? Because may main goal is to be a good investor I am reading these books on Economics just to read the financial pages of newspapers. Maybe it is not necessary to actually learn Economics to be a good investor. The point is I'd like to know something about Economics because people are so afraid, so concerned about what the Federal Reserve, Ben Bernanke what the Central Banks are doing , the interest rates, what the impact of interest rates is on employment, GDP Many of these things may be unnecessary to know in order to be a good investor. I am trying to find a better book on Economics, maybe a book in English... Maybe this book is bad written.