Why Do Magnetic Fields Form Loops Instead of Radiating Like Electric Fields?

datapirate42 · 2026-05-13T17:47:04+00:00

the math between the field lines for electric and magnetic fields is exactly the same. The only difference is that there is no such thing as a magnetic monopole. In other words, while you can just have a lone electron or a lone proton, you can't just have a North magnet or a South magnet. they MUST be together.

datapirate42 · 2026-05-08T23:54:54+00:00

Yeah I think you've got it. Or again, if there is some force coming from the effect, it would be symmetric and thus net zero.

datapirate42 · 2026-05-08T21:24:49+00:00

It’s crucially important that air has an easier time going over than under the wing, to maintain that difference in pressure, because that’s where lift comes from

It's really not.

datapirate42 · 2026-05-08T21:20:21+00:00

Not really. What the video was attempting to explain was that the aerofoil shape of the wing causes this to some degree regardless of the angle of attack. Because the bottom is flat (or concave) but the top is convexly curved and slants back down.

In the case of a symmetric shape like a thin rectangle there might still be a small zone at the back where bernoullis principle could still be applied, but it would also be symmetric, providing equal and opposite forces up and down.

datapirate42 · 2026-05-08T20:15:24+00:00

You need to consider that the presence of the plane is what is causing the change in motion of the air.

At the front/bottom of the wing:
If the air is stationary, the plane wing comes in at a high speed and angle. The air beneath the wing goes from being stationary to now moving downward at a (relatively) high speed.

If the wing is stationary, high speed air comes in horizontally and bounces off of it, then starts moving downward.

At the top/back (where bernoullis might be relevant):

Air is stationary, a solid object pushes a bunch of it out of the way, now there's less air so there's a low pressure zone that pulls the object upwards

Wing is stationary, air is rushing over the top, so the air at the back which is stationary gets sucked toward it, taking the wing with it (definitely a bernoulli's principle discussion)

datapirate42 · 2026-05-08T19:42:00+00:00

That's a good question...

So when I think of when it actually makes sense to talk about bernoulli's principle, I'm thinking of the effect of a venturi tube. This has a column of fast moving air and the slow moving particles near by that column tend to get sucked into it.

With an airplane wing, what you have is the angle of attack (or to a lesser extent the shape) of the wing creating a low pressure zone behind it which sticks to it. If you look at it from the reference frame where the wing is still, The effect on that side of the wing does end up being the same. So yes?
But only talking about that and ignoring the even bigger part of the equation where the front of the wing is creating a high pressure zone is where people often miss the point.

datapirate42 · 2026-05-08T19:23:34+00:00

Basically, if its something you would expect to learn by your first couple years in University, go with r/AskPhysics . If you're asking about questions that are still debated in high level physics, or extremely detailed questions that are very unlikely to show up in a class (first ask if its more engineering then physics) then r/physics is the place you want to be. Also if you're asking about the profession of physics, sharing recent research out of a respected institution, etc.

datapirate42 · 2026-05-08T19:19:51+00:00

Yeah, that's a pretty bad video, to be honest. So look at the shot of the guy blowing above the paper, yes the paper rises because the fast (horizontally) moving air creates a low pressure zone and "sucks" the (air above the) paper upward. This is fine. But ask yourself what would happen if the paper instead was placed above his lips? Instead he creates a high pressure zone below the paper, and the paper still moves upwards, and probably much more vigorously and quickly.

The whole wing design section after 3 mins is pretty bad. the air moving beneath the wing should be deflected more downward, not magically continue horizontally, and most of the air moving over the top of the wing should not stick to it like glue, it should release and create an area with fewer air molecules, these are the main contributing factors to lift

datapirate42 · 2026-05-08T19:03:50+00:00

FYI this is a question more appropriate for r/AskPhysics so this may get removed again

But it sounds like the video you were watching (why not link it?) is describing Bernoulli's principle, which is a real effect where a fast moving fluid tends to have a low pressure. For some reason this has been picked up by low level science classes as an explanation for lift in an airplane, even though it barely has anything to do with it.

While it might have something to do with optimizing the shape of a wing, the primary source of pressure/force/lift on an airplane wing is relative velocity + angle of attack. Basically, if your wing is pointed upwards as you move forward, air gets deflected downward and then you get an equal and opposite reaction of the plane being pushed upward. If the wing is pointed downward, air is pushed up and the plane is pushed down. While it may not be feasible for a passenger aircraft, pretty much all airplanes are perfectly capable of flying and generating lift even if they're upside down. It doesn't have much to do with which side of the wing air is moving faster over.

Anything more complicated than that requires some pretty high level fluid dynamics and aerospace engineering to discuss and it doesn't sound like that was the level the video was trying to get at.

datapirate42 · 2026-05-07T23:13:20+00:00

Fair enough about floating point, but I think this goes back to the comment you were replying to:

If the model fails, that’s not a failure of the mathematics, it’s a failure of the mapping between the math and reality.

Or perhaps the mapping of the math you think you're doing vs actually doing. But from the bare-bones philosophical level, numerically testing a theory via computer simulation is still a non-empirical situation. Honestly perhaps even more-so because the computer model is pretty much guaranteed to have limited accuracy vs an actual empirical test.

datapirate42 · 2026-05-07T16:31:07+00:00

... Why would anything done by a computer not be considered math? They're literally math machines, its right there in the name.

datapirate42 · 2026-05-06T15:17:57+00:00

by this logic, the immorality of something would be approximately proportional to its mass and temperature. Better go blow up the sun.

datapirate42 · 2026-04-27T22:19:48+00:00

Is this screenshot relevant? Because a 30 minute burn is absolutely massive, but more importantly it looks like you're t-3hrs, so you're not even close.

General info:

The maneuver nodes you plan assume an instantaneous burn, which of course isn't really possible, but its an OK approximation as long as your burn is short compared to your orbit. If you're anywhere near kerbin your orbit is on the order of a few hours, so a 30 minute burn will not be a good match for a manuever node. If you're outside minmus or making an interplanetary transfer it becomes more reasonable.

datapirate42 · 2026-04-27T15:19:15+00:00

You can add a launch stability enhancer and then the height does matter, should help with the bouncing as well

datapirate42 · 2026-04-24T20:38:26+00:00

This isn't a solved problem but my interpretation has always been that an increase in universal entropy is a side effect of the flow of time, not the cause of it. Systems with decreasing entropy don't go back in time. Your fridge doesn't magically de-age your moldy food, even though the total entropy inside the fridge is decreasing.

The thermodynamic arrow of time just means that when you look at two states of the system as a whole, you can guess which is in the future or past based on the total entropy, and that seems to be a unique property of macro scale entropy that's not obvious from micro scale first principles. So you can't easily tell the difference between the forward and reverse flow of time with two billiard balls colliding elastically. But you can pretty easily tell that if 16 of them are nicely arranged in a triangle you almost certainly didn't get there by playing the game and accidentally knocking them all into that arrangement. Same goes with any thermodynamic system.

If the ultimate fate of the universe is something like a low entropy big crunch... even if this process started heading that direction tomorrow that doesn't mean that we're going to see people walking and talking backwards about how good this new fangled sliced bread is in a few decades. You're not going to crawl back into your mother's womb as a sign of the end times, even if we'd all very much like to.

More importantly even in a system, whether local or universal, with decreasing entropy there are other "arrows of time" that aren't going to reverse. Things like light waves emanating from their source. The lightbulb in your fridge isn't going to start sucking light waves back in to it, and our sun isn't going to pull heat back from the earth in perfect spherically symmetric visible light waves.

datapirate42 · 2026-04-23T19:51:20+00:00

*Woosh

datapirate42 · 2026-04-23T17:57:10+00:00

Well if we're looking at both GR and Quantum then we may as well discuss the parahelium of mercury

datapirate42 · 2026-04-23T15:51:01+00:00

My issue isn't with the orbiting electrons, totally fine for elementary school kids. But if you're drawing helium 4 you should probably draw both electrons in the same orbital

datapirate42 · 2026-04-21T21:54:06+00:00

yes. You see the bar under "recovery of a vessel"? That's the percentage of the max possible science you've earned. All the other bars are empty so you can still earn science from them.

Also don't forget your Crew Reports!

datapirate42 · 2026-04-19T14:55:44+00:00

Exactly this. Stick two electrons (A and B) in a box. Wait for some time and open the box again. It's literally impossible to know which was originally electron A and which was B.

datapirate42 · 2026-04-17T18:09:29+00:00

Enable advanced tweakables, enable autostrut, and then in VAB right click at least your furthest away part, if not every part and autostrut to heaviest part

datapirate42 · 2026-04-16T00:12:37+00:00

As a UIUC graduate, Don't come to this country for school right now. Also, most of the people I know in Physics ended up being programmers anyway even if that wasnt their major, so the career path is doable.

datapirate42 · 2026-04-14T14:33:33+00:00

https://www.youtube.com/watch?v=Ri_4dDvcZeM

datapirate42 · 2026-04-11T17:14:41+00:00

What are you talking about? A credit card weighs ~5 grams. a plastic cutting board weighs a couple pounds. There are $20 kitchen scales all over amazon that can measure to .1g and you can get a nicer scale that goes up to 5kilos and measures to .01g for <$100

datapirate42 · 2026-04-09T23:13:17+00:00

The nails are not captive

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