Hi, first, I am a foreigner, so please forgive my bad english. That said, I first come from neither physics nor investment, I first studied art, and... well, it was kind of waist of time, then I moved to physics which I handled correctly until I graduated in theoretical physics, but i still feel like I know it very shallowly. Now I would like to perform my own experiments, so I tried to invest some money on the stock market, cause experiments aren't cheap. You know what? I am the worst investor in the world. With the up trend of last months/years, I still lost some money. But I keep hoping I will reach my goal, I try to be more reasonable now, not going in shorting indexes for example, hoping this will collapse brutally. So if you give me some tips, I teach you physics for free! (or just the physics I know, which is much less than THE PHYSICS).
Apart of that, above comments are very good, I also wonder if you want to learn physics for yourself or just "increase" your ability to understand the world in order to make more money, because somebody said that. I don't blame you anyway, but I doubt physics is of any use for usual investing. Physics asks for a lot of dedication, and it's hard to be dedicated by yourself, more if you live in a stressful and rich life like you might. But some people are more skilled than others and you could enjoy it.
I recommend you to focus on some mathematics we learn at university. Differential equations are obviously a master topic, like Fourier series and Fourier transform.
One very useful method to express physical laws is the Lagrangian formulation of physics. You need to know that physics states laws that aim to picture the nature. Most of the laws are "evolution equations", which means it states how a studied quantity evolves through time with respects to some limited varying parameters.
Maths are not necessarily hard in physics, but you need to know them well.
The typical topic someone can enjoy and understand is basic electromagnetism. It has a lot of vector calculus into it, with, at first sight, hard formulas. But you will find them to be quite easy in the end, and you can imagine nice pictures, and a lot of various situations.
Of course before that, it would be good to know Newton's mechanics.
I think to continue with vector calculus you can look at fluid mechanics, and don't be afraid to take a clear maths book about derivation and partial derivatives. There are many things interesting about local conservation laws.
Once you get that you can move to differential geometry, and look at GR and SR. Of course if you follow that path, you will avoid quantum mechanics and optics, and also thermodynamics and statistical physics.
I would suggest you to study quantum mechanics and optics together to see some connections, thermodynamics and statistical physics are somewhat hard and ugly. Most of the theorists likes them. For the thermodynamics I suppose they love it because it's just like learning a whole new science with new parameters, but that still got some very strong laws, without any needs to refer to Newton's ones.
For the statistical physics, it's just... so many calculation, that they like it very hard.
Feynman's book are mandatory.
Good luck!
