Magnets are like magic, every child is at one time fascinated by them. But it's just because it is a stronger field than what we are more used to, and it can both attract and repel.
Magnets are crazy awesome in the sense that they always exist in dipoles. The force between two magnetic poles is analogous to force between two electric charges, so the force between magnetic dipole is also analogous to electric dipole - which means, magnets naturally provide us with a hands-on visualization about how
electric dipoles behave, as well! Meaning that the force between two magnets (small bar magnets) is inversely proportional to the fourth power of the distance.
This means, basically, that when you're handling a bunch of bar magnets, their interactions are actually somewhat analogous to van der Waals forces between some simple diatomic molecules. They don't even need to be polar molecules in the chemical sense (like carbon monoxide) - every diatomic molecule behaves like a dipole to some extent because the electrons in the molecule are almost never perfectly evenly distributed... which creates continuously fluctuating dipoles in some direction. Which enables van der Waals forces even in non-polar substances, like H
2 and N
2, enabling them to have liquid phase at
reasonably high temperatures... even though the effect is much weaker than with truly polar liquids. They fill a container, you can pour them, you can submerge objects in them... by contrast, liquid helium is some
really un-intuitive stuff!
With some effort, you could build a retaining frame to hold some magnets in the shape of water molecule as well. That might be a pretty interesting visualization for physics classes. A box of small and strong enough water-molecule shaped magnets should, in theory, exhibit some similar bonding as water molecules do, with positive poles snapping onto negatives.
Actually now that I think about it, it should be possible to demonstrate other stuff as well with magnets. Like nuclear forces. With a clever configuration of magnets, you could create macroscopic objects that would behave somewhat like protons, others that would behave like neutrons, and you could build simple nuclei from them. You could even demonstrate unstable and stable nuclei, and the nuclear bond energy stored into the system...
Or how crazy is it that gravity doesn't ever actually hurt us here on Earth. It is the impact, not the fall, as so many have pointed out. The field accelerates us, but we don't feel it. We are too small to feel it. The curvature seems flat to us. We only feel the electrostatic forces when we intersect something 'solid', and they are not so forgiving.
I can feel electrostatic forces with the the hair on my arms! Or rather, I can use them to sense electric fields... but that's just another way of saying that an existing electric field exerts a force on the strands of hair on my arms, which I feel by the hair bending...
But the point about touch interaction is another interesting topic.
Turns out that repulsive Coulomb force between the electrons in two objects is just one part of the story. The aforementioned electronic fluctuation in matter causes small dipoles to form continuously, and those dipoles first produce an attractive force (van der Waals again) between the molecules as they approach each other, hence the gekko has enough adhesion to climb the wall and even stay on a roof.
There is also a balance point where the attractive dipole force is overcame by repulsive Coulomb force. However the story doesn't stop there, because it turns out that beyond that balance point, the repulsive force actually increases quite a bit faster than simple electric repulsion would suggest...
...which is fundamentally caused by Pauli exclusion principle.
Basically, when you touch something solid, the molecules on your skin first arrive at the balance point where there's neither attraction or repulsion between them and the foreign object.
If pressure is applied, your fingers don't sink into the object (much), partly because there's an electrostatic repulsive force that pushes against them, but the electrons also repulse each other because they
simply cannot share the same quantum state.
And that's
really sort of spooky interesting to me, because it turns out a fundamentally quantum characteristics of particles is, at least partially, responsible for something as basic as touch interaction.
About the only thing
more freaky is that, apparently, we can
smell the difference between molecules that have different quantum vibration characteristics...
...so if that's true, maybe quantum physics
isn't actually so hopelessly inaccessible to our intuition as we've thought.
Maybe we just need to name quantum properties based on
olfactory qualities instead of
visual qualities like spin or colour charge?
But the gravity of a black hole can kill you, rapidly, unavoidably, before you even reach the singularity. The curvature itself tears you apart in one way, crushes you in the other.
Not if the black hole is big enough!
But hey, talking about visualizing or measuring the curvature of space...
What if you were to build a reasonably large container of known dimensions (a spherical container would be nice for its symmetry), and you would have a way to measure the volume of that container somehow, shouldn't you see a slight decrease in the volume as you send the container from Earth's surface to high orbit, like geostationary orbit?
Only problem is, I'm not sure how to measure the difference accurately enough to get reliable results. One way I thought of would just be gauging the internal diameter of the container by a laser distance meter; another would be to use the container as a microwave resonant cavity and measuring the changes in the resonant frequency.
The point is making the difference in the curvature of space measurable in a way that is sort of intuitively understandable. The question is - how accurately would you need to measure the volume, or cavity diameter, in order to be able to get meaningful results that can be separated from noise and actually correlated with the gravitational potential?
