How to understand an equation physically? I've been reading some Feynman's books. There's a point that intrigues me. It's the fact how we understand a physics equation, not only mathematically, but digging deeply into its roots as a physicist. I'm just a first- year- physics student, but I would like to understand the basic equations I'm studying through its physical meaning, but to be honest I don't really know what Feynman meant. I hope you can help me. For example a equation such as:
F=ma

Thanks!
 A: To work with F=ma physically, just imagine how it plays a role in your daily life. As you rise from bed you are exerting a force on the bed accelerating your body up to a point where you say to your self, just kidding and then sleep in! Physics can be fun, don't let anyone trick you into thinking its a serious subject for serious people. Feynman knew this best.
A: It's helpful to look at an equation about think about what it can tell you.  For instance, if you know that total net force, and the mass, then you can find the accelerations (a=F/m), so this can predict motion.
Similarly if you know the acceleration and the mass you can find out the total net force (F=ma)
Or if you know the force and the acceleration you can find out the mass (m=F/a).  That's already three things you can do with the one equation.
But since it is supposed to be a universal law you actually learn more.  For instance the mass an object had that worked in F=ma for some particular force is the exact same mass that appears later or earlier or when there are different forces.  So the point is that you could use a known force and measure the acceleration on Monday and find the mass then use that same mass (from Monday) and measure the acceleration on Tuesday to learn about the forces on Tuesday.  So you can use those three different ways at different times to learn about masses and forces.
So it's actually saying a lot, it's saying that there is a thing called mass that works on all those different days and that it has the same values on those different days. It says that the same value of mass works for every possible force as well as for every possible location and every possible time.
And by using it to learn about forces there are many things that you can learn about forces.  You can learn what makes each force have the values it has.  You can learn how different forces combine into a total force.  You can notice that forces make thing one and thing two have different accelerations, but that there is something the ma that is the same.  And once you find regularities in a force, you can make additional laws to codify the other things forces do. Such as coming in action-reaction pairs.
