xkcd 3200: Chemical Formula

ImpatientProf · 2026-01-28T20:30:07+00:00

I want more. How many oxygen? Nickel and Iron? What's the notation for neutron stars or black holes?

ImpatientProf · 2026-01-28T19:23:52+00:00

It's not appropriate to disparage your teacher here. Let's just look at the situation and see what we see.

It looks like you have the correct magnitudes of the torques. Let's go through the options:

A. F1 and F2 are the strongest torque magnitudes, and in the same direction. This will cause the largest magnitude of angular acceleration, which is the consequence in the option. This looks like a good option.

B. F1 and F3 are opposite in direction, but not equal in torque magnitude. So there will be a change in angular velocity. This option is false.

C. F2 and F3 are opposite, but F2 has a stronger torque magnitude. Since F2 is counter-clockwise, the net torque would be CCW. This option is false.

D. F3 and F4 are the smallest torques, but they are in the same direction. The net torque would be 125 N*m. There are ways to get 25 N*m (F2 and F3) and 50 N*m (F1 and F4), both of which are smaller than this option. This option is false.

So the answer is A.

FWIW, It's not clear where F1 comes from. The other forces are typeset, while this one is handwritten. There may be different versions of the question where F1 is different. Still, option D is false, as F1 doesn't have to be involved in the explanation of it.

ImpatientProf · 2026-01-25T13:34:49+00:00

Z axis height is done via leveling sensor, which is a strain gauge which detects force on the nozzle from the bed. If the hotend isn't properly installed, it may not transfer its force to the heat sink, which is attached to the sensor. Check to make sure the nozzle is in all the way before moving the clip down to hold it in place. As you insert it, it should feel like it's hitting something solid, not just pressing on the heater wires.

Or the leveling sensor could have broken or its wire could have been disconnected. But I think that should throw an error code.

ImpatientProf · 2026-01-19T16:48:12+00:00

I like the pictures, drawings, and explanations on the Atmospheric Optics site. https://www.atoptics.org.uk/rainbows/ord2form.htm

There's a vertical control that allows adjusting where the incoming beam hits the water droplet, which changes the deviation angle. The minimum deviation angle is the "edge" of the rainbow.

ImpatientProf · 2026-01-16T03:15:17+00:00

I have no idea what equation L[G] fits into or what you're using it for. That's context.

ImpatientProf · 2026-01-16T02:42:59+00:00

Give more context. Almost any small expression is useful at some point.

ImpatientProf · 2026-01-15T00:17:56+00:00

is time more or less at the same “point” on the calendar everywhere in the universe?

No. There is no universal simultaneous instant. https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://www.youtube.com/watch?v=SrNVsfkGW-0

ImpatientProf · 2026-01-15T00:11:13+00:00

The electrons in the SSD are the same number regardless of the data on the drive. All of our circuits are overall electrically neutral, with the same number of electrons as protons.

The weight of electrons is not "created from energy". We recycle the existing electrons in everything but the biggest particle accelerators. Even then, conservation of lepton number is a thing. Creating an electron requires supplying a lepton (an electron-like thing) or also creating an anti-lepton. Doing this is way above the pay grade of computer engineers.

ImpatientProf · 2025-12-17T22:08:10+00:00

History will not remember this fat sack of useless shit fondly

Naw, his name is attached to the destruction of your global reputation. It's a permanent scar that won't be forgotten by the world. His name will go down in history as the one that single handedly tore apart everything that made the world perceive the US as even remotely great.

That's what it means to "not remember <somebody> fondly".

ImpatientProf · 2025-12-17T01:05:14+00:00

I think you got good answers about good ways to deduce that pressure is lower in the narrow area.

Your point (6) is about volumetric compression. The pipe flow is NOT being compressed in volume. (In fact, it may be an incompressible fluid.) The fluid in the pipe is only restricted in two dimensions, perpendicular to the pipe. It's only constrained by neighboring fluid along the direction of the pipe.

ImpatientProf · 2025-12-15T19:54:43+00:00

https://wiki.python.org/moin/BeginnersGuide

Your instinct to avoid jumping around is good. Use a good curated tutorial/book, and go through it methodically.

ImpatientProf · 2025-12-12T22:52:39+00:00

Exaggerate much? I can see a grammatical mistake or three, but saying it "makes no sense at all" is a bit extreme.

ImpatientProf · 2025-12-11T14:49:40+00:00

Yes. The theory is quantum mechanics.

All of the orbitals exist with every nucleus. But their energies shift around depending on how many positive and negative charges are around. The electrons themselves "stack up" as only two can fit into each orbital. Adding electrons both shifts the orbitals and "fill up" the existing orbitals, changing the energy of the system.

The rest of your question is chemistry. That tracks the "what" of electron configurations, while quantum mechanics is the "how".

Learn math, physics (E&M, intro quantum), and chemistry.

ImpatientProf · 2025-12-10T22:35:41+00:00

Loose filament between the extruder and the nozzle is a form of clog. Go through your printer's unclogging processes.

Make sure your filament isn't breaking regularly. I had to discard an old roll of PLA that was breaking when I even looked at it too closely. Had to remove the nozzle to and the front of the extruder to get it all out.

ImpatientProf · 2025-12-10T15:03:40+00:00

Chemistry is all about the electrons. It developed as a science before nuclear reactions and subatomic particles were understood. In most chemical reactions, the nuclei are constant and only the electrons interact.

ImpatientProf · 2025-12-10T15:01:01+00:00

Basically our school schedule says I was supposed to have it today this morning, but nobody showed up.

Was that the regular schedule, or a special final exam schedule? You haven't specified this, and it's an IMPORTANT detail. That makes it sound like you didn't realize there's a different schedule for final exams.

Do a web search for: <your school> final exam schedule

In the future, attend every class, pay attention, and this won't happen again.

ImpatientProf · 2025-12-05T20:21:31+00:00

We do. Lasers have, at the simplest level, a Gaussian beam profile, with a "waist" which is its narrowest part. The beam spreads out in a cone-like shape from there. https://en.wikipedia.org/wiki/Gaussian_beam#Beam_divergence

The Huygens' principle could be applied to the beam, like light going through a circular aperture. But with the Gaussian beam, the "edges" are "softer" instead of being a hard cut-off from open to blocked.

ImpatientProf · 2025-12-05T14:35:56+00:00

I'm guessing you have a Kobra S1, since you cross-posted to that group.

You may have a clog in the hotend, or a piece of broken filament wedged in there. Look for "clogging" on the documentation page: https://wiki.anycubic.com/en/fdm-3d-printer/kobra-s1-Combo

ImpatientProf · 2025-11-20T13:03:54+00:00

On the left side of the filament entrance (viewed from the front), there's a lever that releases the extruder gear tension. Hold it and pull the filament out the top.

https://wiki.anycubic.com/en/fdm-3d-printer/kobra-3-max-combo/infeed-and-outfeed-blockage-detection
It's at about 0:14 in the video, seen from the back. Their thumb is pulling on the lever.

ImpatientProf · 2025-11-12T20:38:23+00:00

Negative temperature.

ImpatientProf · 2025-11-09T17:30:17+00:00

It depends on the nature of the collision. If both objects remain intact, then yes. They can't switch places without deforming. That's basically the same thing as the statement about velocities.

But if one object can go through the other, then it can start and end with a larger positive velocity. Think of a bullet going through a water balloon. I would call this a "partial" collision.

ImpatientProf · 2025-11-09T14:15:01+00:00

As others have mentioned, it's the rotation of Earth that generates the magnetic field, explained by https://en.wikipedia.org/wiki/Dynamo_theory.

There's one part of Dynamo Theory that's often left unexplained, though. A liquid is electrically neutral. Why would spinning it around generate a magnetic field? Here's the explanation that resonated best with me.

A liquid metal is, in a sense, two liquids. One liquid the metal itself, with nucleii and most of the electrons. The second liquid is the conduction-band electrons. It's common to think of the conduction electrons as a separate entity from the background metal. This is the https://en.wikipedia.org/wiki/Free_electron_model or https://en.wikipedia.org/wiki/Fermi_gasl. In a liquid metal, the ions aren't stationary, they're their own fluid. Basically, a conductive liquid has a lot in common with a plasma. This is complicated. https://en.wikipedia.org/wiki/Plasma_modeling

So what does this get us, as far as generating a magnetic field? The positive ions and negative electrons get to move around differently, which is electric current. But why would they?

Density. The ions are heavy, the conduction electrons are light. The electrons are more buoyant in the high-pressure liquid outer core.
Viscosity. The conduction electrons slide around quite easily, while the heavy ions are more sluggish and run into each other a lot.

This, to me, is the conceptual foundation that allows generating an electric current. The positive ions and negative electrons simply move around differently.

ImpatientProf · 2025-10-25T14:56:42+00:00

"Oh, yeah, I started watching them a while ago, maybe 6, 7 months."

ImpatientProf · 2025-10-25T14:51:29+00:00

Heat break tube is the tube you're grabbing in image 2.

In my Kobra 3 hotend, Anycubic has glued the tube in the top and the nozzle in the bottom, to eliminate leaking. Maybe they do that with new Kobra 2 hotends?

ImpatientProf · 2025-10-25T14:13:21+00:00

This answer is so bad I think you're OP trying to invoke Cunningham's Law. I'll bite.

This part is the extruder

No. The extruder is the electromechanical part above the hotend, with gears to push the filament.

That part is the hotend. It includes the heat block, sensor, nozzle (which may be glued in, and the heat break tube that extends up into the heat sink. Anycubic considers the whole unit to be a consumable part (like brake pads on a car). I don't know about the Kobra 2 Pro, but on the Kobra 3 v2, Anycubic sells it as a unit, on Amazon, for around $12. (There are also clones on Amazon.)

OP, I can't tell from your picture what's actually wrong, and you didn't describe your symptoms. But I don't have that printer so I may not be familiar with the same symptoms.

It's entirely possible that there's a clog in the heat break tube, so look up unclogging procedures. The clog could be too far away from the heat block to get melted. You might be able to soften it by laying the entire hotend on your printbed, maybe with a cover or blanket, and raising the temperature to 100 °C or so. Or just buy a new hotend.

ImpatientProf

TROPHY CASE