When thinking about a physics problem or physical process or device, I track which constraints are most important at each step. This includes generic constraints taught in physics classes like conservation laws, as well as things like “the heat has to go somewhere” or “the thing isn’t falling over, so the net torque on it must be small”.
Another thing I track is what everything means in real, physical terms. If there’s a magnetic field, that usually means there’s an electric current or permanent magnet somewhere. If there’s a huge magnetic field, that usually means a superconductor or a pulsed current. If there’s a tiny magnetic field, that means you need to worry about the various sources of external fields. Even in toy problems that are more like thought experiments than descriptions of the real world, this is useful for calibrating how surprised you should be by a weird result (e.g. “huh, what’s stopping me from doing this in my garage and getting a Nobel prize?” vs “yep, you can do wacky things if you can fill a cubic km with a 1000T field!”).
Related to both of these, I track which constraints and which physical things I have a good feel for and which I do not. If someone tells me their light bulb takes 10W of electrical power and creates 20W of visible light, I’m comfortable saying they’ve made a mistake*. On the other hand, if someone tells me about a device that works by detecting a magnetic field on the scale of a milligauss, I mentally flag this as “sounds hard” and “not sure how to do that or what kind of accuracy is feasible”.
*Something else I’m noticing as I’m writing this: I would probably mentally flag this as “I’m probably misunderstanding something, or maybe they mean peak power of 20W or something like that”
When thinking about a physics problem or physical process or device, I track which constraints are most important at each step. This includes generic constraints taught in physics classes like conservation laws, as well as things like “the heat has to go somewhere” or “the thing isn’t falling over, so the net torque on it must be small”.
Another thing I track is what everything means in real, physical terms. If there’s a magnetic field, that usually means there’s an electric current or permanent magnet somewhere. If there’s a huge magnetic field, that usually means a superconductor or a pulsed current. If there’s a tiny magnetic field, that means you need to worry about the various sources of external fields. Even in toy problems that are more like thought experiments than descriptions of the real world, this is useful for calibrating how surprised you should be by a weird result (e.g. “huh, what’s stopping me from doing this in my garage and getting a Nobel prize?” vs “yep, you can do wacky things if you can fill a cubic km with a 1000T field!”).
Related to both of these, I track which constraints and which physical things I have a good feel for and which I do not. If someone tells me their light bulb takes 10W of electrical power and creates 20W of visible light, I’m comfortable saying they’ve made a mistake*. On the other hand, if someone tells me about a device that works by detecting a magnetic field on the scale of a milligauss, I mentally flag this as “sounds hard” and “not sure how to do that or what kind of accuracy is feasible”.
*Something else I’m noticing as I’m writing this: I would probably mentally flag this as “I’m probably misunderstanding something, or maybe they mean peak power of 20W or something like that”