How easy is it to build a simple demonstration at home that proves fundamental law of physics, such as Coulomb’s inverse square law, or Maxwell’s equations? This is one of those questions that always nagged at [Casual Physics Enjoyer] as they sought to find ways to develop a more intuitive understanding of these fundamentals with simple DIY-at-home experiments. Unfortunately this turned out to be rather tricky for Coulomb’s law.
Us H. sapiens – courtesy of a few bright individuals – have figured out many of the fundamentals that underlie this physical world over the past few thousands of years. Even if we still got some pretty massive fundamentals left today for equally bright-minded folk to bash their collective heads against, basics like Coulomb’s law or Maxwell’s equations ought to be a snap now for the average person to replicate since they were after all performed in an era before quantum mechanics, computers or even electrification.
To the dismay of the average physics student, experiments that demonstrate these fundamental laws of physics are still pretty hard to replicate without some solid time and monetary investment. This is demonstrated quite succinctly in the linked article, where the question of how to demonstrate the force between two charged particles, as in Coulomb’s law, and that it is an inverse square relationship is attempted.
Whereas the Wikipedia entry claims it to be a ‘simple experiment’ with just two identical spheres, in a DIY setting this is somewhat tricky, including the part where you have to charge up the spheres and measure the force. Using some aluminium foil and wires you can get the two ends to separate as you’d expect, but quantifying the force is a whole other matter.
if the wet or dry atmosphere is a problem put jar into jar
Please, no. Never Jar Jar.
“Whereas the Wikipedia entry claims it to be a ‘simple experiment’ with just two identical spheres.” Simple to understand and simple to build are not the same thing. Just because the experimental setup is fairly ‘simple’ or straight forward in how it demonstrates the concept, does not mean that the apparatus are simple to build or the measurements are simple to observe. E=mc^2 is a simple equation, yet it took someone like Einstein to derive it because what it embodies is not so simplistic.
E=mc^2 is in fact the simplified version, a special case.
Science is always tricky if you don’t have good measuring instruments. An aluminum foil electroscope is a very crude tool that can serve to demonstrate the principle, but lacks precision.
To test Coulomb’s law one needs something a bit more elaborated, like a torsion balance, which is what Coulomb used.
The “cheap modern trick” version of the torsion balance is just a ball hanging from a very light thread that can only move in a plane (so like, a thin box) and another ball that can be moved towards it. Charge both as much as you can, move one ball to the other and measure the separation as a function of the distance you’re moving in the one ball.
The displacement of the hanging ball from vertical (for small changes) gives you the force (weight of the ball * displacement/length of thread), and then you measure the separation between them. Move, repeat, plot, Bob’s your uncle.
Oops, forgot the trick to determine the behavior as a function of charge! It doesn’t even matter what the starting charge is – you just charge one ball to “something” and then repeatedly cut its charge in half by touching equal size balls to it.
Always admired the Millikan oil drop experiment to determine the charge of the electron. Thought of trying it myself, but haven’t.
“Past few thousand years”? Past few hundred perhaps?
This one is easy.
Take two solid objects and attempt to make them occupy the same space.
Congrats! You just demonstrated the principle.
Coloumbs law isn’t too bad. I think I could do it. It would require a printer and an exacto blade.
Maxwells equations… Yea that’s harder because you have to show a variety of different things. Light is really impractical to demonstrate in a simple way is the biggest problem…
The only thing you need to get from Coulomb’s law to Gauss’s law is that the fields add. Which, if you have a way to demonstrate Coulomb’s law, just requires adding a third charge.
Gauss’s law for magnetism (magnetic fields are divergence-free) can be demonstrated literally with magnets and iron filings. Do whatever you want to map the fields, you’ll never find a divergence. Obviously you run into the issue of “what if there’s some other thing that makes a divergent magnetic field” but this is a real question in physics anyway.
Ampere’s law is easy – it’s the force between two current-carrying wires. The displacement current portion (from Maxwell) is required if you just measure a magnetic field around one of the leads for a capacitor when it’s charging. So you just measure the force between two wires, and measure it again during the charging portion when a capacitor is inserted.
Faraday’s law (magnetic induction) is… make an electric motor or generator.