Measuring software for schools



  • So, I recently and finally got all my stuff of about 80,000 € worth of physics equipment. Naturally, not everything worked right off the bat and some other questions were had.

    For instance, the new multimeters need a 500 mA fuse. But is that a swift, slow-acting or half-slow-acting fuse (couldn't find the proper translation for that one)? Does it matter? The vendor didn't know but he'll get back to me on that one real soon™ (it's been 4 weeks now).

    I also ordered a big, honking demo dynamo / electric motor you can modify in various ways to demonstrate the various effects of permanent magnets versus electromagnets for such gadgets. They should have mentioned, though, that the commutator needs to be in a certain position (vertical) for it to work. In hindsight, it's perfectly clear. Cost me several hours, then again, the sales rep also didn't know about that one at first (had to call an old hand at the company for that).

    I also discovered that I forgot to order a duplicate inductor with 500 coils - the 1000 coils does have a connector in the middle which reduces it to 500 coils. But since the geometry is not identical, you don't get a nice 1:1 current relationship when trying to demonstrate the transformer principle.

    But that's small fry (though I have been astounded by the costs of various equipment - the driver for Franck Hertz costs 4,000€ alone...).

    Because I was also enamoured by the offerings of doing measurements electronically and wirelessly. I mean, it does sound good: You connect the Bluetooth module to the measuring module (e.g. 3D movement/acceleration or current/voltage or electric field strength) and then connect it to a PC in combination with their measuring software. It does look good on paper.

    But the software... first of all, it runs like a dead dog which is still chained to its post. First I thought it was our somewhat outdated school PCs (from 2008). Installed it on my somewhat beefier laptop only to find that I obviously removed the chain but the dog was still somewhat dead. Seriously, as soon as you connect one module the refresh frequency of the program window goes down to 1 second or something - noticable lag between input and reaction. Okay, so maybe it does thrash the CPU (even though I didn't even start measuring anything yet?).

    Nope, CPU rests at a mere 5% above idle. Constantly.

    Next: You have a slight problem if you use more than one module (like, for example, if you want to measure the current through both the primary and the secondary inductor of a transformer?) Because while you can give the modules a name - this name is not used anywhere else. It's still "Measuring Module" and "Measuring Module" in the overview. Granted, you then get "Current 1" and "Current 2" in another selector but those numbers are dependent on the order of connection.

    Then, if you want to do the transformer equations, you naturally want to print the consecutive measurements into one window - that way you see the various proportions for 500:500, 250:500, 250:1000, 1000:250 and their plots in one go.
    And then you want to do that same thing, only for the voltage.
    But, fuck no! there's no: "Delete all measurements" button. There's only a "Delete measurement" one which deletes only the last one. So, now you have to press this button 7 times (with a confirmation dialog, of course). Did I mention that the software eas dead-dog-slow?

    Oh, by the way: They're linking to the bluetooth modules through some homemade solution - which means that every time you connect the modules, you'll also get this "Windows is installing software" popup followed by a "Blutooth module is disconnected" window because they're not using the standard stack (yeah, they don't want anyone to know the PIN - I'm not kidding you, it's actually stated in the manual "You don't need to know the PIN!")

    Then there's stuff like "Integrate the area below the graph" where I haven't found yet if it does anything else but color the area below the graph.

    At least I've found the switch from DC to AC - that one is not obvious as well.

    The same company also offers a video measuring tool - you can use that one if you want to do real-world measurements of projectiles. Simply do a movie of a moving object, include some kind of measuring object (like a staff that's exactly one meter long), define the x- and the y-axis and the framerate and you're done.

    In theory. In practice, you're running into problems like this:

    • no sanity checks - if the object is too slow in the beginning (I did a 120 fps shoot of a free fall) the software decides that because the object hasn't moved a pixel since the last frame that its current velocity is obviously zero. In the next frame it did move. Then not. Then it did. Then not. Which results in a table which has larger-than-zero velocity values alternating with zero values. Oh, well, Excel can filter those.
    • no sanity checks, 2: While you can define areas of the movie as "this is the area the moving object is inside!" it sometimes obviously expects stuff to teleport. In short: The detection algorithm is rubbish and doesn't do any sane predictions - I mean, it does calculate g-forces of about 2000 g sometimes as a result.
    • no support for modern codecs. Seriously, it's either AVI with the built-in Windows codecs (really ancient ones) or MPEG1.

    I asked them about that one and got this answer back:
    "You need to convert into a medium which provides random access to every single frame. Modern codecs are optimized for forward play only. Modern video programs also skip frames if decoding the frame takes too long."

    Yeah, well. With a workflow like that, I won't really use it for my lessons - I mean, if it takes 10 minutes for my pupils to do such a conversion, load it into the program and so on, it doesn't really work for "spontaneous" movement examinations.
    And for stuff I myself prepare? Naw, for the problems I'm working with there are lots of professionally edited videos so I won't use that one either...



  • @Rhywden said:

    I obviously removed the chain but the dog was still somewhat dead.

    +1


  • mod

    @Rhywden said:

    I obviously removed the chain but the dog was still somewhat dead

    +1



  • @Rhywden said:

    But is that a swift, slow-acting or half-slow-acting fuse (couldn't find the proper translation for that one)? Does it matter?

    Swift is safer for the equipment. Slow-acting reduces the chance your fuse will burn out if there's a "blip" in the power.

    I don't know why you'd ask the equipment maker this, as it's kind of just your choice. (You've never had to replace fuses in your car or anything before?) I can pretty much guarantee if they get back to you at all, they'll say "swift-acting" because that'll potentially save them a warranty repair.



  • You'd ask the manufacturer because only they know the equipment's tolerance to transient voltage spikes.



  • Yeah but he's always gonna say to go with the fastest fuse available. So there's no point in asking.

    Whether to follow or ignore that advice is up to you. For an expensive piece of equipment, I'd be inclined to follow it. For, say, home lighting? Better to not be annoyed by constantly false-alarm fuse burnouts.



  • @blakeyrat said:

    Yeah but he's always gonna say to go with the fastest fuse available.

    Not necessarily. Some kinds of things have a big surge of current when you turn them on (or at other times, whatever), and if you use a fast-acting fuse it will blow every time you use it. Such things generally explicitly specify a slow-acting fuse, but maybe they forgot.



  • I'd say if that were the case, it's 100% likely that would be mentioned in the manual/documentation. But ok, fair enough, that is a point.


  • Discourse touched me in a no-no place

    @blakeyrat said:

    For, say, home lighting? Better to not be annoyed by constantly false-alarm fuse burnouts.

    Or you could move out of the 1930s and fix your wiring.



  • @FrostCat said:

    Or you could move out of the 1930s and fix your wiring.

    At least stick a penny in there.



  • 1927, thank you very much.


  • SockDev

    Then you could at least get into this century?



  • You gonna loan me $1,500 to hire an electrician?


  • SockDev

    @blakeyrat said:

    You gonna loan me $1,500 to hire an electrician?

    No, which is why I asked the question rather than arrogantly assumed you should just get on and do it.



  • I see, but at the same time I want you to give me free money.


  • SockDev

    Yes, I'd like that too. I'd like free money, but sadly no dice. The universe has not conspired, for example, to align the numbers drawn in the lottery with the numbers I choose on the rare occasions when I buy a lottery ticket. In the meantime I just have to suck it up and carry on with the software I'm writing in the hopes of selling it to make some money, or failing that get a proper job again.



  • @blakeyrat said:

    Swift is safer for the equipment. Slow-acting reduces the chance your fuse will burn out if there's a "blip" in the power.

    I don't know why you'd ask the equipment maker this, as it's kind of just your choice. (You've never had to replace fuses in your car or anything before?) I can pretty much guarantee if they get back to you at all, they'll say "swift-acting" because that'll potentially save them a warranty repair.

    The reason I'm asking is because those are multimeters which are then put in the hands of pupils. Which means that it's more than likely that someone will not get the meaning of "0L" (which I myself didn't get the first time) and put more current through than they're meant to.
    Yes, you can tell them about that until your tongue turns blue. Someone will still not get the relationship between "This is a 6 V lamp" and "Don't increase the voltage beyond 6 V!" (instead going: "This lamp is quite bright, isn't it?")

    With that in mind, a slow-acting fuse would reduce the chance of me having to get the screwdrivers in order to replace the fuse. While a fast-acting one would probably better protect the multimeter's electronics.

    That's why I was asking. And, yes, if they tell me to get swift ones then I'll do that.



  • Oh, and I forgot one thing: You need to update the firmware of the BT modules whenever the measuring software is updated. Now, I have 8 of those modules.

    Connect them all and update the firmware at the same time? Nope, will fail at some point.

    Connect them all and update the firmware consecutively? Nope, will still fail at some point.

    Only solution: Connect one, update the firmware, disconnect it, connect the next one...



  • I don't know if this has anything to do with this particular line of products, but I've had my share of college friends who were either electrical or electronics engineers and they couldn't code shit. Hell, some even struggled to use a computer. It's not their fault of course, because it's not their job when you should have a few software engineers doing the UI and all that.



  • @Rhywden said:

    "This is a 6 V lamp" and "Don't increase the voltage beyond 6 V!"

    When we moved factories my big boss decided to help by wiring up a large inspection light to the mains...it was a 12V halogen.

    I was facing the other way and it looked like a nuclear weapon going off in a Michael Bay film.

    He was extremely surprised by the results :)



  • In case anyone wants to see this in real life:

    Halogen lamp overload – 01:19
    — MrTurboturbine



  • You completely forgot that a multimeter that's worth its salt (i.e. say a Fluke, Amprobe, Agilent, or Gossen Metrawatt, vs. the cheap janky Chinese meters that go by too many names these days) is going to use HRC (High Rupture Capacity, IIRC) fuses instead of the normal, dinky tubular glass ones. This is because a HRC fuse will just quietly blow if you do something dumb with the meter like put it across a 277/480Y circuit while set to measure current, while a 5x20mm glass fuse is likely to attempt blowing, then turn into a tiny arc lamp, then go on to set the meter on fire! The downside is that HRC fuses are a bit costlier and harder-to-get.



  • @Rhywden said:

    For instance, the new multimeters need a 500 mA fuse. But is that a swift, slow-acting or half-slow-acting fuse (couldn't find the proper translation for that one)? Does it matter?

    Yes, it does matter. Measuring current with a multimeter is actually a difficult job for a multimeter. That's why most multimeters either don't have a current range or it's very limited - miliamps on a multimeter that can measure hundreds of volts.

    You need to teach your students what a difficult job this is for the equipment. The way to to this is to get the fastest, most sensitive fuse you can. This should protect your expensive equipment from students and when it does blow (mutiple times in one class) then the students will learn to be very careful with a multimeter set to measure current.

    Do NOT keep the spare fuses in the classroom. Make sure the student has to walk to the supply store which is at least down the end of the hall, if not in the next building. By making the student who blew the fuse do this walk of shame, you will burn it into their memory and they may eventually become a good electrical engineer who understands how fragile the current setting is on a multimeter.

    Of course you get to use the good equipment with current shunts and sensors that don't blow out with too much current when you do your demonstrations at the front desk. You don't want an accident causing you to send a student out for a spare fuse and make the rest of the class wait.

    Transformer demonstrations? I never got that in school. The teacher just gave us the transformer ratio equation and just told us that's how it works - no demonstration to prove the teacher wrong with those pesky geometry constraints.



  • @Cursorkeys said:

    wiring up a large inspection light to the mains...it was a 12V halogen.

    I learned the difference between series and parallel, and that one measures current by putting a meter in series with the load, not across the supply, at a fairly young age. I was playing with my father's multimeter (cheapie Radio Shack, fortunately). I knew how to measure voltage, but I decided to measure the current through a light bulb. It's unlikely the meter would have survived even if I had done it correctly; I think the meter was probably 125mA full scale, and the bulb was probably 60W (500mA) or 100W (833mA). However, connecting a current meter directly across a 120V supply capable of delivering 20A or more, well, my father was not pleased with the condition of his meter when he got home. :anguished:



  • @tarunik said:

    You completely forgot that a multimeter that's worth its salt (i.e. say a Fluke, Amprobe, Agilent, or Gossen Metrawatt, vs. the cheap janky Chinese meters that go by too many names these days) is going to use HRC (High Rupture Capacity, IIRC) fuses instead of the normal, dinky tubular glass ones. This is because a HRC fuse will just quietly blow if you do something dumb with the meter like put it across a 277/480Y circuit while set to measure current, while a 5x20mm glass fuse is likely to attempt blowing, then turn into a tiny arc lamp, then go on to set the meter on fire! The downside is that HRC fuses are a bit costlier and harder-to-get.

    My pupils are only dealing with power supplies with a maximum of 12 V and 1 A.

    The rest of the stuff (like the Braun's tube, the electron ray gun or the Franck Hertz driver) does not need additional meters, has dedicated ones or the current is limited to the mA area (for instance, my big plate capacitors are connected to the 10 kV power supply only through a 1 MOhm resistor.)



  • @Qwerty said:

    Yes, it does matter. Measuring current with a multimeter is actually a difficult job for a multimeter. That's why most multimeters either don't have a current range or it's very limited - miliamps on a multimeter that can measure hundreds of volts.

    You need to teach your students what a difficult job this is for the equipment. The way to to this is to get the fastest, most sensitive fuse you can. This should protect your expensive equipment from students and when it does blow (mutiple times in one class) then the students will learn to be very careful with a multimeter set to measure current.

    Do NOT keep the spare fuses in the classroom. Make sure the student has to walk to the supply store which is at least down the end of the hall, if not in the next building. By making the student who blew the fuse do this walk of shame, you will burn it into their memory and they may eventually become a good electrical engineer who understands how fragile the current setting is on a multimeter.

    Of course you get to use the good equipment with current shunts and sensors that don't blow out with too much current when you do your demonstrations at the front desk. You don't want an accident causing you to send a student out for a spare fuse and make the rest of the class wait.

    Transformer demonstrations? I never got that in school. The teacher just gave us the transformer ratio equation and just told us that's how it works - no demonstration to prove the teacher wrong with those pesky geometry constraints.

    Sorry, I don't believe in that kind of stuff. If I did wait every time a single student did something wrong, I'd never get anything done. They have to pay for the fuse and that's it.

    The consequence in my physics and chemistry classes is that it's reflected in their grades. And that their experiment didn't work. Making the rest of the class wait? I'd only be punishing myself because we have only so much time to teach stuff and the department of education doesn't care why you didn't teach the stuff you were supposed to teach.



  • @Qwerty said:

    You need to teach your students what a difficult job this is for the equipment. The way to to this is to get the fastest, most sensitive fuse you can. This should protect your expensive equipment from students and when it does blow (mutiple times in one class) then the students will learn to be very careful with a multimeter set to measure current.

    Did you not read my reply above? Because if you just pick a fuse based on rating and speed (time to blow) alone, you're an idiot who deserves to have their meter set on fire because the wimpy fuse you put in couldn't break the circuit when it tried to blow. Interrupting rating is actually the most important rating for a meter fuse, considering the kind of abuse meters encounter, especially at the hands of students.

    (FWIW: I might have blown a multimeter fuse once during my whole time as a Computer Engineering student; I couldn't tell if it was anything I could have done though, or if the fuse was dead by the time I tried to use it.)

    @Qwerty said:

    Do NOT keep the spare fuses in the classroom. Make sure the student has to walk to the supply store which is at least down the end of the hall, if not in the next building. By making the student who blew the fuse do this walk of shame, you will burn it into their memory and they may eventually become a good electrical engineer who understands how fragile the current setting is on a multimeter.

    I'd probably be OK with keeping them in the classroom, but I'd make the students do their own fuse changes in front of the rest of the class. (Being able to check/change the fuse(s) is multimeter maintenance 101 in a nutshell.)

    @Rhywden said:

    They have to pay for the fuse

    QFT, especially for fuses like the ones I linked above. A proper meter fuse (I linked the Cooper Bussmann DMM series above, but fast-acting 600VAC/DC midget fuses such as the Cooper Bussmann KLM series can be used in meters that are CAT rated to 600V max in any category) isn't going to be cheap, but you get what you pay for.

    @Rhywden said:

    My pupils are only dealing with power supplies with a maximum of 12 V and 1 A.

    Doesn't stop 'em from screwing with the meter and a mains socket.



  • @tarunik said:

    Doesn't stop 'em from screwing with the meter and a mains socket.

    The cables they have don't fit into the mains socket and if they actually manage to pull that one off, they'll be out of our school faster than they can say: "short circuit".

    That is, if they survive the experience.



  • @Rhywden said:

    The cables they have don't fit into the mains socket and if they actually manage to pull that one off, they'll be out of our school faster than they can say: "short circuit".

    That is, if they survive the experience.

    What, no meter probes? :P



  • @tarunik said:

    What, no meter probes?

    As I attested earlier, meter probes fit mains sockets rather well. :EMOJI_NOT_FOUND:


  • Discourse touched me in a no-no place

    @Rhywden said:

    The cables they have don't fit into the mains socket and if they actually manage to pull that one off, they'll be out of our school faster than they can say: "short circuit".

    That is, if they survive the experience.

    WAT

    In High school I took 3 inches of solder, bent it into a U, and stuck it in a mains socket. (Remember the US only has 120V). All that happened was most of the solder disappeared, and a molten ball skittered across the desk, leaving some slightly interesting scorch marks. Now, if your meters are expensive, that may be one thing, but in general that sounds like a harsh response.



  • @HardwareGeek said:

    As I attested earlier, meter probes fit mains sockets rather well.

    This I know firsthand, having had to use the nearest live wall socket as a reference voltage for making sure AC V still works on several occasions, as well as using the meter to answer the "is this outlet working?" question.

    @FrostCat said:

    Now, if your meters are expensive, that may be one thing, but in general that sounds like a harsh response.

    Actually, an expensive meter is likely going to be CAT (category) rated to III or IV for use around the AC mains. My DMM, for instance, is CAT III 600V/CAT II 1kV to the best of my recollection; it's also been around for a couple of decades or so.

    The basic rules of thumb when probing mains or anything else that can bite go as follows:

    1. Use CAT rated probes (a CAT rated meter will come with proper probes, but you need to be careful when shopping for aftermarket probes)
    2. Keep your fingers behind the finger guards on the probes (as that's why they are there)
    3. If you are checking if a circuit is turned off, do a "live-dead-live" check: measure a known-good outlet/... with your multimeter, measure the circuit in question, and go back and measure the known-good outlet again. This makes sure that your volts function didn't go kaput on you in the middle of it all -- in fact, the only 'send it back to the manufacturer to have it fixed' failure I've seen on a DMM is a dead AC V range; the manufacturer fixed it no-questions-asked, and under warranty, even!


  • @FrostCat said:

    WAT

    In High school I took 3 inches of solder, bent it into a U, and stuck it in a mains socket. (Remember the US only has 120V). All that happened was most of the solder disappeared, and a molten ball skittered across the desk, leaving some slightly interesting scorch marks. Now, if your meters are expensive, that may be one thing, but in general that sounds like a harsh response.

    Over here it's 230 V. Secondly, you're not alone and someone else can be hurt by your horsing around. Thirdly, I laid down the law: No horsing around during experiments. Fourthly: My ass is on the line if you or someone else gets hurt and I can't prove that I didn't enforce the rules. Fifthly: You've just demonstrated that you're not willing to follow the rules, that you don't care what happens to me or your fellow pupils and that you can't be trusted.

    I won't have such pupils in my lessons. That's the one rule I'm absolutely and seriously unwilling to bend in any way.

    #You follow the safety instructions or you're out.

    And if you're so stupid as to actually deliberately circumvent safety measures then you're shit out of luck, at least at this school. I actually couldn't care less as to what happens to you - I'm thinking of the other who may just happen to be caught in the crossfire. And if I catch you pulling such stunts you'll think a planet fell on you.



  • @HardwareGeek said:

    meter probes fit mains sockets rather well

    Same here in Australia. This is how I learned to be not so terrified of mains power, just careful.



  • @Rhywden said:

    You follow the safety instructions or you're out.

    Geez, you're no fun. We used the 100V DC power supplies to shock forearms on unsuspecting classmates while they were busy doing what they were meant to be doing instead of fucking around. I have no idea why they had 100V DC power supplies but they were good fun.



  • @tarunik said:

    The basic rules of thumb when probing mains or anything else that can bite go as follows:

    Use CAT rated probes (a CAT rated meter will come with proper probes, but you need to be careful when shopping for aftermarket probes)
    Keep your fingers behind the finger guards on the probes (as that's why they are there)
    If you are checking if a circuit is turned off, do a "live-dead-live" check: measure a known-good outlet/... with your multimeter, measure the circuit in question, and go back and measure the known-good outlet again. This makes sure that your volts function didn't go kaput on you in the middle of it all -- in fact, the only 'send it back to the manufacturer to have it fixed' failure I've seen on a DMM is a dead AC V range; the manufacturer fixed it no-questions-asked, and under warranty, even!

    @Arantor, this is what I was talking about.

    zzzzzzzzz


  • Discourse touched me in a no-no place

    @another_sam said:

    Geez, you're no fun.

    I get the idea that you should prevent your charges from doing stuff that will run the actual risk of serious harm (as in, things that could maim, but are really hard to do don't count.) But shocking people or putting solder in mains outlets, that's more or less harmless fun.

    One of my high school teachers dug out a Van de Graaf generator and let us form a human chain out into the hall so we could shock people.


  • SockDev

    @boomzilla said:

    @Arantor, this is what I was talking about.

    zzzzzzzzz

    And you even read it to the current post to be able to tell me you fell asleep in it, awesome.



  • @FrostCat said:

    I get the idea that you should prevent your charges from doing stuff that will run the actual risk of serious harm (as in, things that could maim, but are really hard to do don't count.) But shocking people or putting solder in mains outlets, that's more or less harmless fun.

    One of my high school teachers dug out a Van de Graaf generator and let us form a human chain out into the hall so we could shock people.

    I'm not so enamoured by the idea of molten metal running around uncontrollably.


  • Discourse touched me in a no-no place

    @Rhywden said:

    I'm not so enamoured by the idea of molten metal running around uncontrollably.

    It's about 2 drops, it moves a few feet, then falls off the table, falls to the floor, and solidifies. This is solder we're talking about, I'm not suggesting someone short the socket with solid iron. Also we did it in a classroom, not a lab, so even if that drop of solder could potentially hurt, say, a CNC lathe, well, that wasn't in the room.



  • I don't really care what you think is "harmless". It's molten metal not under your control and you're playing with a mains line.

    That's two strikes.

    You can horse around in private all you want. During my lessons? Not by a long chance.


  • Discourse touched me in a no-no place

    Your choice. It strikes me as a pantywaist attitude, though. I mean, seriously, literally the worst that could happen would require you to guess which way it would go, and then put your eye right in the path, and get it right. Remember, I said I agreed with you about things that are not just potentially dangerous, but have a reasonable chance of being actually dangerous. Someone sticks a fork in an outlet? Yeah, that's a problem. An inch of solder? Harmless.

    Plus, look at it this way: a zero tolerance attitude is going to make it forbidden fruit. OTOH, you let the students do something that's theoretically dangerous, but practically speaking perfectly safe, they're going to do exactly what we did: try it about twice, and then never do it again because it's not actually very interesting.



  • Oh, right, this "If we forbid something it will be doubly interesting!" myth.

    Following that particular logic, all youths will be criminals at some point just because we forbid stabbing someone with a knife.

    Or to make the point more clear: Using your logic, I also should let them experiment with sticking a fork into an outlet. Because that's also forbidden under my rules.

    Again: It's my responsibility to see that you don't come to harm. Because I am legally responsible for any kind of bodily harm in my classroom. I'm dealing with a lot of very dangerous stuff on a daily basis and, frankly, I don't need that kind of headache.


  • Discourse touched me in a no-no place

    That was a pretty stupid reductio ad absurdum.

    I've done a LOT of things people told me not to do. Generally I don't do things that run the risk of jail time, though, because, like most people, I'm not bereft of reason.


  • Discourse touched me in a no-no place

    @Rhywden said:

    Or to make the point more clear: Using your logic, I also should let them experiment with sticking a fork into an outlet. Because that's also forbidden under my rules.

    Only if you're the kind of person who can't be bothered to read what your debate partner actually wrote, because I have repeatedly said things that have actual chances of actually being dangerous are distinct. IOW: you stick a fork in a socket, you're gonna have a bad day. You stick a bit of solder in there, there's not really any way something bad can happen without deliberate intent. I've only said that about 3 times now, so maybe you should keep reading this paragraph until that sinks in.

    Unless you've been borrowing @blakeyrat's shoulder aliens or somethings.



  • Off the top of my head: You yourself said that the solder will move a few feet and will fall to the floor.

    So, then it could easily jump off the table and fall onto a foot where someone is wearing a shoe that is open at the top.

    Bam, instant injury.

    That, by the way, is also the reason why we have a "No sitting while we're doing chemical experiments" rule.
    @FrostCat said:

    That was a pretty stupid reductio ad absurdum.

    I've done a LOT of things people told me not to do. Generally I don't do things that run the risk of jail time, though, because, like most people, I'm not bereft of reason.

    Yes, and because I myself don't do things that run the risk of jail time, I don't let my pupils mess with mains.


  • Discourse touched me in a no-no place

    @Rhywden said:

    So, then it could easily jump off the table and fall onto a foot where someone is wearing a shoe that is open at the top.

    Bam, instant injury.

    There's a really good chance it will have a solid surface before it gets to floor level, and it'll only weigh a gramme or so as it won't all liquify at once. The amount of injury will be small. In fact, I'd guess that they're at more risk from the overreactions as they try to get out of the way; lab benches are very solid and can hurt fast-moving limbs.

    Worry about other things first, OK? But feel free to bust the ass of anyone who horses around like this as the next time, they might do something more dangerous like using copper wiring.


  • Discourse touched me in a no-no place

    @Rhywden said:

    So, then it could easily jump off the table and fall onto a foot where someone is wearing a shoe that is open at the top.

    You let people wear open shoes in a lab situation? That's TRWTF. People in that class got actual burns from soldering irons. A drop of solder would be relatively minor.

    @Rhywden said:

    Yes, and because I myself don't do things that run the risk of jail time, I don't let my pupils mess with mains.

    Once again, this is a stupid comparison.


  • Discourse touched me in a no-no place

    @dkf said:

    Worry about other things first, OK? But feel free to bust the ass of anyone who horses around like this as the next time, they might do something more dangerous like using copper wiring.

    Ugh. Nobody there was that dumb. We deliberately used things that wouldn't short out the mains. Are you people entirely without a sense of proportion?


  • Discourse touched me in a no-no place

    @FrostCat said:

    We deliberately used things that wouldn't short out the mains.

    Shouldn't matter. There are circuit breakers, yes?


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