Perhaps a question that is too naive to be on Physics.SE but I let the experts here decide (and downvote at will), but there seem to a certain company that claims to have created what it calls a "magnetic generator" where, if the machine is powered externally long enough (which is in seconds or minutes) allowing an electro-magnetic contraption to reach a certain RPM, it can start producing enough electricity to keep turning the contraption, without the aid of the external power while generating surplus electricity. This sounds like perpetual motion machine, yet a bit "snake oilish". The website of this company is done very professionally, they have some slick youtube vidoes -- but scamsters can and do pull impressive illusions off. Is there plausible physics behind this setup ?  Please note that I have no interest in the company or the product, but quite interested to know if there is some real physics behind it.  Here's a  that describes the product.
I know that a perpetual motion machine (a device that produces work without an energy source) would violate several physical laws, the first that comes to mind being the . I also understand that a claim that perpetual motion is possible would probably not be congruent with the scientific method, occum's razor, etc.  What I am interested in is whether there exists some logical and intuitively meaningful (to they lay person) demonstration that perpetual motion is universally impossible, based only on axioms rooted in observable physical phenomena, rather than the obvious reasons why it is merely improbable and incompatible with some of our physical laws.  Certain violations of physical laws, such as travelling faster than the speed of light, can be shown to be unlikely as they would cause paradoxes or logical impossibilities, such as a . In that instance, the axioms needed to establish a paradox (time dilation) are empirically observable, and a counter-claim would require the existence of new paradox-resolving laws that are not established, or the permission of paradoxes which is difficult to imagine.  Conversely, the idea that some invention is impossible on the basis of its violation of a physical law alone is difficult because it requires a .  So, without relying on the assertion that a physical law is omnipresent (e.g. conservation of energy), is there some impossibility or logical paradox that would arise from the existence of a machine that could produce work without indefinitely without an energy source?  Finally, I'm very aware that perpetual motion is a bit of a dirty word and will likely touch a nerve with people, so please take the time to let me know how I can make this question less offensive and avoid the inevitable down-votes.
When I cd a link, my current path is prefixed with the link's path, rather than the path of the directory the link links to.  E.g.  ~/dirlinks/maths$ ls -l logic lrwxrwxrwx 1 tim tim 71 Jul 27 10:24 logic -&gt; /windows-d/academic discipline/study objects/areas/formal systems/logic  ~/dirlinks/maths$ cd logic ~/dirlinks/maths/logic$ pwd /home/tim/dirlinks/maths/logic  ~/dirlinks/maths/logic$ cd .. ~/dirlinks/maths$   I would like to have my current path changed to the path of the linked dir, so that I can work with the parent dirs of the linked dir as well. Besides ls the link to find out the linked dir, and then cd into it, what are some simpler ways to accomplish that? For example, after cd into a link, how do you change your current path to the path of the linked dir? I am planning to visit the UK on a USA travel document but there’s nowhere I am able to find information about visas: I’m a Zimbabwean but using a USA refugee travel document do I need to apply for a UK visa before I travel or I can they just give them on arrival. How large would the steam explosion at Chernobyl have been? So the  of the HBO series began to cover the  that led to them sending three divers into the water below the reactor to drain the tanks.  This occurred after the initial explosion that destroyed the reactor, and after the fire in the core had been put out. But at this point the decay heat and remaining fission reaction kept the core at more than 1200°C, causing it to melt through the concrete floors below the reactor.  And below the reactor were water tanks which contained 7,000 cubic meters of water (according to the TV show. If anyone has a real figure, I'd love to hear). When the lava of the melted core hit it, it would cause an enormous .  Finally, my question: About how large would this explosion have been? The character in the show says "2-4 megatons" (of TNT equivalent, I assume). I'm pretty sure this is absurd and impossible. But real estimates are hard to come by. Other sources vary wildly, some repeating the "megatons" idea, and others saying it would've "". This still seems crazy.  tl;dr:  I know a lot of it hinges on unknowns and the dynamics of the structures and materials involved, so I can simplify it to a constrained physics question:  Assuming 7,000 cubic meters of water instantly flashes to steam, how much potential energy is momentarily stored in that volume of steam occupying the same volume as the water did?  I don't know what to assume the temperature of the steam is. There were hundreds of tons of core material at temperatures near 1200°C, so worst case scenario you could assume all the steam becomes that temperature as the materials mix. Best case scenario, I guess we could assume normal atmospheric boiling point (100°C)? How do I create a partially transparent flag? What did my neural network just learn? What features does it care about and why? Why does my user number show up in the search box when clicking my profile information? Irfanview nearest equivalent for linux How do I go about proving this?  If $\gcd(a,b)=1$ and $\gcd(a,c)=1$, then $\gcd(a,bc)=1$. I'm very confused with gcd proofs. Finding the number of non-negative integral solutions of $x + y + z = 10$ Prove that $n^3=n \text{ mod }6$ for every integer $n$. Prove that for every integer $n$ , $n^3=n \text{ mod }6$  I was having no clue how to do this, then I thought of case-by-case analysis and obviously it worked. The problem is that there were six case and together they are long.   Is there any shorter method of proving this. Kindly provide some hints. Is the 64-Bit version of Ubuntu only compatible with AMD CPUs? I was told that computers with more than 2 gig's memory need a 64 bit operating system to utilize all RAM.  Is the 64bit Ubuntu download really JUST for AMD processors? I am asking because the disk image I downloaded says AMD64.  So will my new Intel 2.3Ghz Core i3 Dual Core processor work with 64 bit Ubuntu?  It runs the 64bit version of Windows without any qualm. To find all $n$ such that $(n-1)!+1$ is a perfect power of $n$ How to find all positive integers $n$ such that $(n-1)!+1$ can be written as $n^k$ for some positive integer $k$? From the man page on git-merge, there are a number of merge strategies you can use.     resolve -  This can only resolve two heads (i.e. the current branch and another branch you pulled from) using 3-way merge algorithm. It tries to carefully detect criss-cross merge ambiguities and is considered generally safe and fast. recursive -  This can only resolve two heads using 3-way merge algorithm. When there are more than one common ancestors that can be used for 3-way merge, it creates a merged tree of the common ancestors and uses that as the reference tree for the 3-way merge. This has been reported to result in fewer merge conflicts without causing mis-merges by tests done on actual merge commits taken from Linux 2.6 kernel development history. Additionally this can detect and handle merges involving renames. This is the default merge strategy when pulling or merging one branch. octopus -  This resolves more than two-head case, but refuses to do complex merge that needs manual resolution. It is primarily meant to be used for bundling topic branch heads together. This is the default merge strategy when pulling or merging more than one branches. ours -  This resolves any number of heads, but the result of the merge is always the current branch head. It is meant to be used to supersede old development history of side branches. subtree -  This is a modified recursive strategy. When merging trees A and B, if B corresponds to a subtree of A, B is first adjusted to match the tree structure of A, instead of reading the trees at the same level. This adjustment is also done to the common ancestor tree.   When should I specify something different than the default?  What scenarios are each best for? Functions which are Continuous, but not Bicontinuous What are some examples of functions which are continuous, but whose inverse is not continuous?  nb: I changed the question after a few comments, so some of the below no longer make sense. Sorry. Set the QGIS display to show decimal degrees? Using QGIS 2.6.1 Brighton. I am trying to set the CRS for the project to display Decimal Degrees, where it is defaulting to Feet. I can change it in the Properties Dialog, but it does not change it, it is just staying on Feet. How do I change it?  Edit: this layer was imported from a shapefile where it was internally set to Feet. I was able to get the vendor to supply one with Decimal Degrees so my problem is gone. Still would love to know if there was a way to do it myself from within QGIS. How can I modify the size of swap with LVM partitions? "method driver /usr/lib/apt/methods/https could not be found" update error sudo apt-get update E: The method driver /usr/lib/apt/methods/https could not be found. michael@Ubuntu:~$ sudo apt-get clean michael@Ubuntu:~$ cd /var/lib/apt michael@Ubuntu:/var/lib/apt$ sudo mv lists lists.old michael@Ubuntu:/var/lib/apt$ sudo mkdir -p lists/partial michael@Ubuntu:/var/lib/apt$ sudo apt-get clean michael@Ubuntu:/var/lib/apt$ sudo apt-get update E: The method driver /usr/lib/apt/methods/https could not be found. E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it? michael@Ubuntu:/var/lib/apt$ sudo apt-get update E: The method driver /usr/lib/apt/methods/https could not be found.   Why am I getting these errors when doing an apt-get update? How do I get started with RAW photography? Having read about the benefits of shooting in RAW as opposed to JPEG (for example ), I'd like to have a go with it myself. However, I'm not really sure how to go about it.  I can turn RAW mode on in my camera (that's easy!), but what do I do with the files when I get them on to my computer? I presume I need to process them to get the RAW data into something that I can work with, but do I need a specific tool for my camera (a Finepix S5100), or will something like the GIMP do what I want? I'm also a little confused about how I then take advantage of the abilities that RAW gives me when I'm processing it on the computer — do RAW processing tools have more processing options than standard tools? Profile Bug - Reputation Summary Not Displaying All Lines I've upgraded from 4.4.0 to 4.4.8 and then 4.5.2 on Ubuntu 16.04 LTS 64-bit, and it's still happening.   At 4.5.2 it's even more frequent, and mainly in Chrome (haven't tried firefox or opera just yet). Every time I open a new web page. Any way to fix that, or is it a bug?  00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) 04:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Venus XTX [Radeon HD 8890M / R9 M275X/M375X] (rev 81)   Cheers.