# Danijel Gorupec

Senior Members

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2

1. ## Electrical Energy

Sorry for being late, but I thought it might be insightful to invoke some caution regarding the above reasoning. The fact that windings in slots are out of the position of maximum field is, I would say, an understatement. Indeed, I feel it would be better to say that windings in slots are in position of insignificant field. All the iron that surrounds the wires acts as a good magnetic shielding - iron takes the large majority of the flux and very little of it actually goes through wires. As a result, the majority of motor torque cannot develop in the wires - and it is not that wires are pushing on the iron and turn the rotor around. Of course, placing windings into slots helps them not to slip sideways (it also helps fasten them against much more significant centrifugal forces). In addition, it enables motors with narrower air gap - if placed on the surface, wire dimensions would add to the air gap (and, as Studiot said, immersed into considerable field of the air gap they would then also feel considerable sideways forces). The third quoted sentence is the debatable one... A current-carying wire develops a force proportional to the field it is immersed into. The idea of 'number of filed lines it cuts' might come useful sometimes, but to me it seems somehow artificial (and confusing). It is just the field 'through' the wire and the current in the wire that counts (actually, it is just the quantity and velocity of electrons and the field density and its direction at their path). As the filed density is quite low inside deep motor slots, so the wire there cannot feel much force - no matter how much field lines it cuts. The majority of rotor torque must be generated in the iron itself - in rotor 'teeth', specifically. The purpose of the rotor winding is to generate field gradient where 'teeth' are immersed into... This is how I see the torque generation in a modern electric motor... You might get quantitatively good enough results if you just make calculations where you simply multiply rotor winding current and field density in the iron (or in the air gap, but not in the slots where winding actually is). However, such a procedure does not describe what actually is happening inside and might confuse a student who tries to think rigorously.
2. ## Ancient Mars, water or ice?

That is why I agree with you that if there was liquid water on Mars, for most of the time it had to be covered by ice. However for brief times of increased volcanic activity, some of that ice could melt down exposing liquid water... but I am just talking staff, I have no real knowledge here.
3. ## Ancient Mars, water or ice?

While I tend to agree with you, I just want to notice that volcanic activity could supply greenhouse gases.
4. ## Birds flying farthest from place to place.

My understanding is that arctic terns make stops during migrations (at least by 'landing' on water, if not on the land)? I don't know what would be the longest hop for a bird that normally lands (that is, those that do not eat and sleep on wings). I know however that a common swift might not land for months. My understanding is that a common swift can migrate to South Africa, spends few months there and then return to Europe without ever landing. (Metallica comes to my mind... "we're off to never never land").
5. ## Local conservation of energy

Thanks Markus, I will try to read about the stress-energy-momentum tensors and then maybe I will ask for some additional clarifications. At first look the subject seems very difficult. BTW, what do you mean by "the energy inherent in gravity itself"? I am worried if it needs to be treated separately.
6. ## Local conservation of energy

I have questions about local conservation of energy. I am trying to better understand consequences that follow from it. How I understand it, the 'local conservation' means that not only energy is conserved, but is conserved in every local region. It cannot just at once decrease in one region, and increase in a region far away without anything happening in between. So, is the local conservation of energy a true law? It seems correct to me, but I cannot remember if I ever heard about it during my formal education (looong time ago)... [BTW, is it also valid regarding quantum mechanic? Specifically what I have in my mind is the wave function collapse - does the collapse has at all anything to do with energy distribution?] Next... My understanding is that one of direct consequences of the law of local conservation of energy is that we are then capable to define a value of 'energy flow' (through space) and a value of 'energy density' (in space). Am I correct? I have troubles understanding this 'energy density'. How much is this distribution of energy throughout space a physical thing. Should I expect that with a very sensitive equipment I should be able to measure a curvature of space that this energy density is producing... thus actually measuring energy density? (I understand that energy density should curve the space as well as mass do). Is energy density tied to one frame of reference or is it the same in all frames of reference? It seems to me that if you change the frame of reference, the energy density distribution changes too. Take for example a kinetic energy. Really, "where" is the kinetic energy? I mean, how is its density distributed in space? Where is gravitational potential energy? Where is electrostatic potential energy? I guess, If the energy density is for real, it should be possible to answer these questions. No? I guess energy density could be in fields. For example, kinetic energy could be distributed in gravitational field of a massive object (its mass increases with speed). For electrostatic potential energy I even know some formulas that say how energy is distributed in electric field... But what do you say?
7. ## So who's going to win the world cup?

Germany, I am afraid. As I am getting older, I am only hoping to see some good moves and good players (like 2014. James Rodriguez goal). I do not attach much to national team any more.
8. ## Prehuman industrial civilization on Earth?

What about nuclear waste - do you guys believe that after 10M years it will still be possible to tell that a nuclear waste site is clearly of an artificial origin? My opinion is that it strongly depends on the circumstances. As far as I know, there is almost nothing that would surely last 10M years. However, even very fragile things can last that long under right circumstances (like a mosquito in amber). My opinion about OP is then: we know that happy circumstances happen and some artifacts do get preserved for amazingly long time. I therefore find it very unlikely that there was any industrial pre-human civilization - for sure we would find something. We didn't even find fossilized biological remains of an 'animal' that would look like a candidate (and it seems that to make an climate-changing industrial civilization you need quite a sizable population). Concluding industrial civilizations just from a rapid temperature rise is indeed a 'creepier conclusion'.
9. ## The law of conservation of energy is the greatest mistake of physics

Sorry, this took a wrong turn... I was only making a joke... I found it amusing how you constructed your sentence saying that 'engineers never noticed devices that did not work'. I, on the other hand, noticed that almost all my first (and second) tries did not work. Still have some of them hidden in my garage. Going on-topic... ummm.... ummm.... nope.
10. ## The law of conservation of energy is the greatest mistake of physics

Hey Bender.... But many do not work. We tend to hide them (in embarrassment). We only put forward those that do work
11. ## Venezuela

Inappropriate (at best) and short-sighted (even if well-intended) politicians, sure... But are you sure that you mean 'politicians' and not 'Venezuelan voters'? [ I ask because I think that sometimes posters are trying to be polite blaming politicians when they actually think people. ] High politics in Venezuela was, in my opinion, plainly wrong. But this is nothing new for me. It is the non-existence of any effective corrective action coming from the society that I find intriguing. In fact, I am afraid that the opposite is happening - the movements are such that the society undermines itself. The fluctuations on oil market, being an external factor, can be attributed as a trigger, but again no coping mechanism is being established, as far as I can see. How not? One would expect that societies adjust. [ Venezuelans are a large group of people, not just a few individuals, and for sure they are neither smarter nor stupider than any other nation in average. I am sure that an average citizen just does whatever he/she can to improve his/her own life and surrounding and also the life of those he/she cares about... Maybe we can say "they got what they asked for", but probably we cannot claim that we would make better choices. ]
12. ## Venezuela

Maybe it is a boring theme, but if someone wants to comment, I will be happy to read. What do you think is happening to Venezuelan society? Can this be called a degradation? Or is this only a fluctuation on path of progress? Or is this actually a progress when looked from a different perspective? Or is it just a logical consequence of some external pressure? To me, Venezuela is an interesting example to study as it has plenty of natural resources. My personal opinion is that this already can be called degradation. When I look at individuals in this society I understand that the each individual strives for the better. Yet, the society as a whole spirals downward. I find this fascinating... What is the 'invisible hand' that governs this process? Is there some sort if bad ideology that individuals pursue leading them in wrong direction? Or is it that most individuals just make logical and reasonable decisions at personal level and it still pushes the society in the wrong direction? Maybe you think that what happens in Venezuela is a progress (on society level). How come? I don't see it. Some societies in north Africa did turn toward democracy, and for those societies I could accept such argumentation (barely) despite the fact that currently they are in quite a chaos - but I just don't see it for Venezuela. Do you think that it is actually external pressure of some sort that causes present society movements in Venezuela (I guess, some Venezuelans would say this is true blaming greedy Americans for disruption of their society). But I myself don't see much of some external pressure (is there more behind scenes that I can imagine?). External pressure is always present, and most societies can cope with this. I have no connections with Venezuela. My interest is academic (but also personal because I find historical events like Fall of Rome quite upsetting).
13. ## Air moving in long tube

In any case, I will have sensors at both ends so it is only the matter of weighting factors. Normally the regulation will be agonizingly slow, but there might be situations (after power interruption, for example) when a quick re-establishment of air flow will be needed - and this is when latency could be an issue. (There are 4 fans of 0.8MW always working in parallel as a single unit - it would be cumbersome to transport a single 3MW unit and it would lack redundancy. I however think that not even half of the installed power will ever be needed.)
14. ## Air moving in long tube

Thanks Studiot... In my application there is a 3MW fan pushing air into tubes that feeds the air toward tunnel boring machines (TBM). I was puzzled because there was a claim that an air-speed sensor nearer to the fan will be able to sense air-flow changes much sooner (faster response regarding the fan speed) than if it is placed at the far end of the tube. I however tend to believe there will be no relevant difference (it is a slow regulation process anyway), and you seem to confirm this.
15. ## Air moving in long tube

Probably I should know the answer, but I have doubts... There is a very long tube (pipe), say 2 km long and 3 meters in diameter. The tube is open at one end and there is a stationary air inside and outside the tube at normal pressure and temperature. At the other end of the tube there is a piston. At one moment the piston starts moving with some constant velocity (much lower than the speed of sound) something like 5m/s. My question is how long does it take that the air at the open end of the tube starts moving at speed comparable to the piston speed? My guess is that this would happen quickly (comparable to the time sound needs to travel the distance). Am I right? Will there be oscillations of air speed at the open tube end (if yes, on what will oscillation frequency depend)? More difficult question for me to guess... There is the same setting as above but the piston is not moving at constant velocity, but is pressing the air with some constant force (that is, it creates constant local pressure of the air). How will now look the air-speed curve (speed-vs-time) at the open end of the tube? Will it lag significantly to the air-speed curve near the piston? No need to make actual calculations - I am only trying to qualitatively understand what is happening. No need to consider high piston velocities either. Thanks.

17. ## When do AIs become moral agents?

Great, great argumentation Sensei... +1... (I myself have a simple stance that we can have morality issues when switching off an AI only if that AI has a will to live.)
18. ## Danijel Gorupec

Ha :)... 400 posts and counting... Tremble Swansont, tremble.

19. ## Migrating HD to new laptop

Thank you guys for your helpful comments. I solved the problem within 24h by buying a second-hand laptop similar to the one I had (Lenovo; similar specifications; similar age; the dead laptop was 'L' line, the current laptop is 'T' line) and migrating the hard drive into it. Finished successfully, after some manual driver installations. Windows is working good; all other important licenses also seem to work. Prior to this, I bought external HD enclosure and made backup (as StringJunky suggested) just in case something goes wrong. I also tried to boot my HD from a newer (more recently manufactured) laptop, but this did not finish good as this newer laptop model required something called UEFI boot. I see now that this second-hand laptop that I obtained has a very poor battery... nevertheless, my software is running and I am as happy as a pig
20. ## Migrating HD to new laptop

I hope my software licenses (rockwell automation, for example) are tied to hard drve. At least some od them. Replacing the motherboard may cause windows license problem then, if i underatood correctly? I still have to confirm that i can find mb replacement. I was trying to find the same laptop. No success for the moment.
21. ## Migrating HD to new laptop

Yes, this is my secondary option. My prmary is to boot from my old disk as i have some hard to replace software licenses on it.
22. ## Migrating HD to new laptop

Motherboard died on my laptop (lenovo think pad). If I buy new laptop and replace its hard drive with the one from my old laptop, is there a chance that it will boot? Is it worth a try? How to increase my chances?
23. ## When do AIs become moral agents?

Maybe... when it asks you not to do it (or shows other signs that it does not want to be switched off, like fighting for its 'life').
24. ## New Forum Design?

Not bad... I am reading this on a big screen - a design is a bit too wide for my taste. I am missing side content (list of new posts and user feeds) - is there any way to have them again? Where can I read user feeds? Also, I look a bit too pale on my avatar picture. I actually have a bit grayish complexion.
25. ## Effects of EMP (For Sci-Fi Book)

Just some ideas: - you might 'invent' a new type of battery that is extensively used in electric cars. The new battery has all the benefits (gasoline cars being quickly replaced, even banned for years) but also one drawback - sensitiveness to EMP (military should avoid its use in military vehicles). - you might consider that smaller batteries of that type (cell phones) are less sensitive to EMP. Or maybe, it is still possible to find and use classic-type batteries for replacement in cell phones (no such replacements for electric cars). - There could exist microwave (or whatever) energy links between Moon and Earth (sort of power lines) that actually directed and maybe amplified the effect of the Moon-originated EMP. - Flying a space shuttle becomes a heroic mission due to all the debris (satellite network being all crushed generating lots of space garbage).
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