/ Things you don't understand but wish you did

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TobyA 31 Aug 2019

Many years ago on a Friday afternoon UKC discussion it somehow came up that I didn't know why the oceans are salty. This had clearly never been taught to me at school and then I had gone another couple of decades never really thinking about it. Someone expressed surprise that I didn't know this (I have a feeling it might have been Dave Garnett, but I could be wrong on that) but went on to explain in simple clear way, which has helped me explain to other people since.

Even longer ago than that, back when the internet was still young (and Google wasn't yet the only game in town), I was researching how easy it actually is to build a nuclear weapon, and it was UKCers who explained to me what maraging steel is and what an air cooled lathe is, and how much one costs (surprisingly little on the second hand market as I remember).

Anyway, other people must have things they want to understand but don't. Ask and let's see if the UKC collective can still offer useful, non-judgemental and accurate answers!

My big question is can someone please explain to me how my induction hob in the kitchen works? A friend who is an electrical engineer and a Finn tried but failed (and either or both of those might be important to the failure). I still don't get why if the circle bit of hob which my coffee maker or saucepan isn't touching doesn't get hot, then why don't I get an electric shock when I touch the coffee maker? Yes I know, ridiculous sounding if you do understand I'm sure!

Post edited at 10:58
balmybaldwin 31 Aug 2019
marsbar 31 Aug 2019
In reply to TobyA:

When you put a pan of the right kind onto the hob (which is a changing magnetic field) the electrons in the pan go for a bit of a dance around within the pan.  There is a teeny bit of electricity involved, but the main thing is that the pan gets hot.  The electrons aren't going anywhere like they would in a circuit. There isn't really a circuit as such, the only transfer from the hob to the pan is magnetism, glass is not a conductor of electricity.  

The hob only works with really good magnetic materials so if you put a copper pan on the hob it doesn't work. Same with your fingers.  

The "dance" is called an eddy current.  It's rather like an eddy on a river, it goes round and round and doesn't flow downstream.  

Post edited at 11:34
TobyA 31 Aug 2019
In reply to balmybaldwin:

That's a bit like my mate's explanation. I sort of know it's a magnetic current but don't really get how that heats a pot up! Why doesn't it heat up other steel things nearby but not touching it? My GCSE physics obviously didn't cover that in 1989.

TobyA 31 Aug 2019
In reply to marsbar:

Dancing electrons - I can get with that. Do you teach science by any chance Marsbar?

marsbar 31 Aug 2019
In reply to TobyA:

I think anything else steel would have to be right on the hob to heat up.  

marsbar 31 Aug 2019
In reply to TobyA:

Maths.  But my degree is engineering.  I've spent so long teaching SEN recently and it shows!

Post edited at 11:37
cb294 31 Aug 2019
In reply to TobyA:

Induction hobs work like  transformers, where a high voltage alternating current generates a magnetic field in one coil. This alternating magnetic field then "induces" a corresponding current in a second coil, hence the name.

Voltage and current change with the ratio of the number of loops in each coil. E.g. in a standard power supply for, say, a toy train or low voltage appliance, the mains side has a high number of coils, high voltage but a low current. This gets transformed, on the output side (with a low number of loops) into a low voltage but a high induced current.

In the case of an induction hob, the conducting base of your pan corresponds to the lowest possible number of "loops" on the output side, resulting in a high current through the pan bottom, essentially a short circuit.

It is this "induced" current which heats the metal of the pan. The ring of the hob is not itself heated, and will feel cool because the glass like material on purpose does not conduct heat very well. Also, the induced voltage is too low to give you a shock (and the conductivity within the pan much better than through your body).

The same principle is used a larger scale to recycle steel, where strong magnets induce so much current in the scrap metal that it eventually melts.

CB

marsbar 31 Aug 2019
In reply to TobyA:

I think there is some A level chemistry involved as well.  The way the electrons are in different materials means iron pans will work well and copper pans won't work.  

2
marsbar 31 Aug 2019
In reply to TobyA:

Anyway, why is the sea salty?  I missed that too.  And why are humans the same amount of salty as the sea?  

1
TobyA 31 Aug 2019
In reply to marsbar:

> Anyway, why is the sea salty?  I missed that too.  And why are humans the same amount of salty as the sea? 


Humans I don't know, but the sea is salty because evaporation removes water from the sea but not all the minerals that are washed in through rivers. This is why the Dead Sea is so salty: because it is below sea level the only way water gets out of it is via evaporation - so all the minerals are left behind and are salts (form salts? - I'm a bit fuzzy on that bit!). It also accounts for why you can if necessary drink from the Baltic and you won't get salt poisoning (although having lived next to it for a long time, I know that pollution, particularly but not solely from St Petersburg make drinking it not a great idea regardless of salt levels!). There is so much fresh water into the Baltic, and being a cold area of the world, very little evaporation, the salinity levels are much lower than say the Atlantic.

Did I get that one right folks?

TobyA 31 Aug 2019
In reply to cb294:

> resulting in a high current through the pan bottom, essentially a short circuit.

> Also, the induced voltage is too low to give you a shock (and the conductivity within the pan much better than through your body).

I think this is the bit I need to get my head around to stop half expecting to get a shock when I pick up the coffee pot! ;-)

So it's voltage that gets you, not current, in terms of electrocution? I do remember vaguely learning about this at school but it's a long time ago! Child #1 is doing really well in physics at school so if I can drag him away from computer games for a bit he'll probably explain it to me!

Postmanpat 31 Aug 2019
In reply to TobyA:

 I don't understand how, by refusing to watch the final hours of last week's test match, I ensured that I didn't jinx it and that England won. I know it is so but don't understand how.

Also, I don't understand how quarks seem to influence each other from huge distances. Could it be the explanation for the "cricket effect"?

john arran 31 Aug 2019
In reply to Postmanpat:

Thank you for not watching the match. It was brilliant!

Johnhi 31 Aug 2019
In reply to Postmanpat:

> Also, I don't understand how quarks seem to influence each other from huge distances. Could it be the explanation for the "cricket effect"?

Armed with a years old physics degree I've never used, I'm not sure that real world quarks do influence each other from huge distances so perhaps they're not the culprit.  The potential energy associated with separating the two quarks would be sufficient to generate further quark anti quark pairs and you'd just end up with 2+ new particles rather than your original bound quarks.

plyometrics 31 Aug 2019
In reply to TobyA:

I wish I understood why some people take the time to pick up their dog’s shit, put it in a poo bag, then proceed to hang it on a tree branch for someone else to deal with...

Post edited at 13:05
Jack B 31 Aug 2019
In reply to TobyA:

> So it's voltage that gets you, not current, in terms of electrocution? 

Close, it's actually a bit of both. What actually does the damage is current, specifically current flowing through the heart and surrounding muscle. But a person has quite a high resistance, so a large voltage is needed to push the current through the person (Ohm's Law). 

A low voltage but high current example would be a car battery. You can get impressive sparks and melt spanners with them, but the low voltage means that they are not usually dangerous. Your induction hob is in this category, the small voltage makes currents flow in big slabs of iron, but not in you.  A high voltage low current example would be a static shock. The voltage can be thousands of volts, but there is almost no current, so even though the current does flow through you, it doesn't do any harm. Mains has a large enough voltage to overcome the body's resistance, and can provide large currents, which is why it's dangerous to shove forks into wall sockets.

There are a couple of other features of induction hobs which haven't been mentioned too. The magnetic field they produce is carefully shaped to only extend into the area above the coil, so nearby metal objects are not heated (though leaving a fork right next to the pan is still not wise), and they can measure the amount of energy being absorbed by the pan.  If the pan is removed, if a pan of the wrong type or size is used, the energy flow will be wrong and the hob will switch itself off. 

Post edited at 13:06
yeti 31 Aug 2019
In reply to TobyA:

Well... I have a lathe but I don't think I've ever heard of the phrase "air cooled lathe"

also ... I don't understand how people get so excited about politics 

and ... why can you still think while being shot with a tazer, when all your muscles lock up?

jon 31 Aug 2019
In reply to Jack B:

When I were a lad I was taught 'it's the volts that jolts but the mils that kills'. Is that right?

wercat 31 Aug 2019
In reply to TobyA:

If you've ever been into something mains operated shortly after it has been running you will find that the mains transformer gets warm or even hot.  In this case too it is eddy currents heating the magnetic core.  Transformer metal cores are laminated in layers to reduce the eddy currents by providing gaps in the core across which the eddy currents cannot flow.

The reason for the eddy currents are the constant reversal of current by AC either from the mains or from a specific AC generator circuit.   The constant reversal means a constantly reversing/changing magnetic field and a conductor placed in a changing magnetic field will have a current induced in it which in this case will constantly be reversing direction.  

Unlike electromagnetic waves magnetic fields have generally a much shorter range  (though they can be employed for underground communications - eg cave rescue radio) but like any electric current the eddy currents have a heating effect in the conductor in which they are induced.  The lower the resistance of the conductor the less heating resulting from resistance.

Post edited at 15:03
Chris Craggs Global Crag Moderator31 Aug 2019
In reply to TobyA:

Did you know that the Med gets more saline and hotter the further east you go (away from the Atlantic) due to heating/evaporation. Despite being hot, the water is so dense it sinks to the floor and flows back west. The Med basin is filled to the lip of the Straights of Gib with warm saline water which spills over and sinks into the cold Atlantic eventually fanning out as a lens of hot salty water, with cold water above and below, when the densities are equal. (I did an OU unit on Oceanography years ago - one of the more interesting things I learnt).

Chris

doz 31 Aug 2019
In reply to plyometrics:

> I wish I understood why some people take the time to pick up their dog’s shit, put it in a poo bag, then proceed to hang it on a tree branch for someone else to deal with...

I think that's cos of quarks as well... apparently it then breaks down into tiny bits and statistically anywhere you go in the universe there will be small particles of other people's dogshit...this is why I prefer to stay at home these days

Timmd 31 Aug 2019
In reply to plyometrics:

> I wish I understood why some people take the time to pick up their dog’s shit, put it in a poo bag, then proceed to hang it on a tree branch for someone else to deal with...

It doesn't explain the logic, but the 'why' is because humanity is infinite in all aspects,  weirdness, badness, goodness, funniness, quirkiness. I've been a lot less surprised/perturbed since I concluded humanity is infinite. Most of the time.

Post edited at 15:40
Jack B 31 Aug 2019
In reply to jon:

> When I were a lad I was taught 'it's the volts that jolts but the mils that kills'. Is that right?

Pretty much. Higher voltages give more of a jolt (like static, which can be 20000V), but don't directly cause harm. Mills = milliamps is current, and about 10-20mA through the heart can kill.

Exposure time also matters, 300mA arm-to-arm for 10ms wouldn't do much, but 5mA for 10 seconds would cause significant muscle contractions.

Post edited at 15:52
Bob Kemp 31 Aug 2019
In reply to Postmanpat:

I'd add most of quantum physics, astrophysics, nuclear physics etc.. Always fascinating, frequently incomprehensible...

Bob Kemp 31 Aug 2019
In reply to Jack B:

The weird thing is that at even higher levels, the prospects of survival actually increase (if you get help quickly enough), basically because the heart seizes up. It's the ventricular fibrillation at the mid-levels that kills. 

Jack B 31 Aug 2019
In reply to Bob Kemp:

> The weird thing is that at even higher levels, the prospects of survival actually increase [..] basically because the heart seizes up. It's the ventricular fibrillation at the mid-levels that kills. 

Which is how defibrillators work! Take a heart which is in ventricular fibrillation as a result of an electric shock or heart attack, and give it a 25A 10ms shock (roughly, different machines have different profiles) and it will stop completely. But then there is a very good chance that it will start correctly again.

Which is also why defibrillators are only really useful when the casualty is in ventricular fibrillation - not if the heart has stopped completely. Fortunately the smart ones being installed in stations etc. can tell if the casualty needs a shock or not, and can even tell someone what to do they don't. They are pretty cool bits of kit actually.

marsbar 31 Aug 2019
In reply to Jack B:

Very much.  

As someone in a rural area where it can take a while to get an ambulance out its great to see them popping up everywhere.  

Bob Kemp 31 Aug 2019
In reply to Jack B:

Ah, thanks, I was wondering if there was a connection.

itsThere 31 Aug 2019
In reply to marsbar:

A magnetic field and dancing is one of the best explanations ive seen that also works for RF/microwave frequencies.

Tom V 31 Aug 2019
In reply to Timmd:

Yawning. Why is it infectious?

In fact, why should typing the first word of this post get me at it?

(And a few of you, probably).

marsbar 31 Aug 2019
In reply to Tom V:

Something to do with humans being in groups and picking up on each other’s behaviour so they all sleep at the same time.  Not sure of details. 

hokkyokusei 31 Aug 2019
In reply to yeti:

> and ... why can you still think while being shot with a tazer, when all your muscles lock up?

Because the brain isn't a muscle.

Dax H 31 Aug 2019
In reply to plyometrics:

> I wish I understood why some people take the time to pick up their dog’s shit, put it in a poo bag, then proceed to hang it on a tree branch for someone else to deal with...

I think I have sussed this one out, a tiny minority pick it up and leave the bag to collect on the way back, some forget though. 

As for the rest my theory is that during the time taken for the dog to squat and do what they do other dog walkers will probably see you so they whip out the bag and pick up the poop. Whilst walking carrying the bag it takes a friction of a second to dump it in a bush when no one is looking. These people are a separate breed to the rest of us called scummy bastards. 

Rog Wilko 31 Aug 2019
In reply to Postmanpat:

>  I don't understand how, by refusing to watch the final hours of last week's test match, I ensured that I didn't jinx it and that England won. I know it is so but don't understand how.

I was pretty sure if I watched it I'd jinx it but decided no-one would know it was my fault, so watched it anyway, knowing that if it did turn out to be an amazing win I would have seen it live rather than a recording where I already knew the result. It was great, but I do wonder if the deaths from heart failure that afternoon were above average.

Ron Rees Davies 31 Aug 2019
In reply to marsbar:

> Something to do with humans being in groups and picking up on each other’s behaviour so they all sleep at the same time.  Not sure of details. 

Not just humans though. Go to a zoo and yawn at the primates and they'll start too. Even some dogs yawn in response to owners yawning. 

cb294 01 Sep 2019
In reply to TobyA:

No, voltage by itself is irrelevant. You either have to electrically fry the neurons in the brain and the heart muscle cell (e.g. using a US electrical chair, roughly 3000V DC and a LOT of power behind it, or electrocuting yourself with railway power lines while train surfing, 15kV here on the continent and again plenty of power to maintain a nice arc for a while befor the circuit breaker cuts in), or use a lower voltage in short pulses (often AC) to throw your heart out of beat (the propagation of heart muscle contraction from atrium to ventricle works by ion currents between the muscle cells).

As a child's prank, we used to take the piezo igniters from spent cigarette lighters to give people little electric shocks. This is entirely harmless, despite the sparks operating at around 50.000 V. This range of voltage is also often reached when you get a shock from a wooly jumper.

CB

Timmd 01 Sep 2019
In reply to marsbar:

> Something to do with humans being in groups and picking up on each other’s behaviour so they all sleep at the same time.  Not sure of details. 

It's related to the development of empathy, too, apparently children don't yawn in response until around the age of 3 - or whenever psychologists say that empathy starts to develop (I think that's age 3?). Funnily enough I yawned in response to Tom V's post. 

Post edited at 07:25
Tom V 01 Sep 2019
In reply to Timmd:

Nice to have empathic internet mates (yawn) 

JuneBob 01 Sep 2019
In reply to Jack B:

Heart disease is the leading cause of death I think, so why doesn't everyone have a defibrillator at home?

Oceanrower 01 Sep 2019
In reply to JuneBob:

Because, if you did, heart disease wouldn't be the biggest killer. Cancer would be.

And then you'd have to have a chemotherapy machine at home as well.

And if you did, cancer wouldn't be...

Etc.. etc..

Post edited at 10:13
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marsbar 01 Sep 2019
In reply to JuneBob:

They are expensive.  

But we have a couple in our village now, and trained volunteers.  It's a great idea. 

In fact I'm going to make a new post. 

Post edited at 10:44
TobyA 01 Sep 2019
In reply to yeti:

> also ... I don't understand how people get so excited about politics 

My PhD was done for a dept. of politics and I worked for a decade at an international politics think tank, so I guess I should have a go at that one!

For some people (me included), following politics in other countries that don't directly affect my life is just interesting, in a way some people find football interesting and I just don't. I'm amazed by the level of obsessive interest some of my colleagues have in football - it's genuinely impressive how much they know and remember about the game. And I don't know why I'm not interested at all, but I follow US politics in the same way - I just find it really interesting, and as I've tried to understand what happens and why, I've learnt more and more about the history of the US as well. To a certain extent we all need hobbies, and that accounts for the interest - at times of high drama, Presidential elections for example, it is for me genuinely exciting, like a cup final is for a footy fan I guess.

On UK and EU politics, I have a lot more 'skin in the game' and it feels to me at least that I can't not be interested. Of my immediate family of 5, 3 are not British citizens and until, probably, October 31st they have had as much of a legal right to live, work, and go to school here as me and my youngest child who is like me also a British citizen. Being directly affected by the uncertainty is "exciting" in the same way that being a long way out on an ice pitch, where the ice turns out to be too thin or two soft to take convincing ice screws is "exciting"! I would always argue politics affects everyone in some ways and that's a reason to take an interest in it, but I accept that some people are more insulated from changes brought about by the government than others, so the political system might feel more remote to them.

cb294 01 Sep 2019
In reply to yeti:

> also ... I don't understand how people get so excited about politics 

I cannot understand this sentiment. Politics is about shaping our societies, our future, that of our children and indeed that of the planet in general.

If there is one thing one should get excited about it is politics, especially in "interesting" times like these!

I appreciate that the daily grind of politics, especially at local and council level, can be amazingly tedious and is hard to get excited about. All the more reason to thank those who get actively involved and run for office. Again, locally it can be badly paid or even not at all (by office I include jobs at local level in parties, not only in government or parliament), and nothing would work without these volunteers. 

CB

Rog Wilko 01 Sep 2019
In reply to yeti:

> also ... I don't understand how people get so excited about politics 

..... in common with an increasing number of people over my lifetime. Until the 2017 election turnouts for parliamentary elections have been on a downward trend for many decades. I agree with cb294 (above) and would argue that politics is in everything to some degree. People (usually Tories in my opinion) who say "Why do the left have to bring politics into everything?" would disagree and would like to think there are large areas of public life which should be political no-go areas because "common sense" (as they see it) should decide what is said and done. Today, unfortunately, large numbers, it seems, of even the well-educated young to middle aged have no knowledge of or interest in politics, and this is really bad for the country and society as it makes it easy for determined groups (such as extreme right or left, or pro-Brexit groups, for example), to have an influence beyond what they would have otherwise. It is amazing how many well-educated people do not even understand how an election is decided, or how a government is formed or how it falls, or what the opposition is or what the shadow cabinet is, etc. etc.. But they still have the vote if they choose to use it. I can't decide if compulsory voting (as in Australia) is a good thing, as the ignorant (I'm not using this as a pejorative) are more likely to be swung by simplistic populist arguments. What I think should be in the school curriculum is something like old fashioned civics, which could mean more chance that everyone will have the basics. Sorry, this is turning into a bit of a ramble, so I'll stop.

yeti 01 Sep 2019
In reply to TobyA: and cb294 and Rog Wilko

Yeah, I do understand your points, I do watch the world news and I'm interested in what other countries do politically

the ones i find weird are the footie fan kind of support, the people who can rant for hours when they have no way of changing anything

I once delivered some posters to a labour election office and they were very creepily excited by them

 I also don't really get the level of feeling some people have for football

and I don't get swept up by the atmosphere, like some people say you will

thing is I remember Wilson and Heath, they seemed to alternate wasting public money 

Tom V 01 Sep 2019
In reply to Rog Wilko:

I always wondered how a subject like civics could be taught with any degree of impartiality: I'm pretty sure I couldn't have done it.

marsbar 01 Sep 2019
In reply to Tom V:

We do some of it in PSHE or whatever its called this week.  Citizenship maybe? 

It's about the process of voting and the mechanics of law making. We don't really get into the party politics. 

Tom V 01 Sep 2019
In reply to marsbar:

Ha ha! Like your rider about PSE. 

Don't you think there are some areas of teaching, though, where your own particular ideology might impinge on the content you are expected to present to a bunch of learners?

Tom V 01 Sep 2019
In reply to TobyA:

Just been listening to Che Gelida Manina on Classic FM. 

How come practically all Puccini arias have me sobbing before twenty seconds are out?

WaterMonkey 01 Sep 2019
In reply to TobyA:

I don’t understand how people get excited about fireworks, let alone why someone would pay for them.

Tom V 01 Sep 2019
In reply to WaterMonkey:

I used to get excited about tossing a few 321 Zeros about and manufacturing the odd threepenny rocket bazooka way back in history but cant understand the tolerance of the waste and pollution shown for New Year's Eve type celebrations. 

And sleeping out in my little caravan overlooking Manchester last weekend I was amazed by the number of inpromptu  skyrocket launches visible from my viewpoint . Almost as if a message system was in operation.

marsbar 01 Sep 2019
In reply to Tom V:

I mostly try to give them the tools to figure it out for themselves.  For example spurious correlations is a good way to encourage questioning fake news.

I did lose it when I asked the children to research and present Fibonacci and one of them had the funniest picture of Donald Trump's hair.  

marsbar 01 Sep 2019
In reply to Tom V:

I've just realised you meant generally.  I'm sure in other subject this must be the case.  

Tom V 01 Sep 2019
In reply to marsbar:

Yes. Probably more in Humanities than Science and Maths. I would have thought Religious Education (as was) and History most susceptible.

TobyA 01 Sep 2019
In reply to Tom V:

I trained to teach Citizenship and now teach RS, Sociology, Philosophy and some citizenship. The kids amuse themselves in the first year trying to guess what religion I am - they come up with some pretty amusing guesses, but I tend to put them out of their misery at some point and explain I'm an atheist.

Teaching citizenship through Brexit has been interesting, but actually it's easier if you are teaching the GCSE as there is a set content that they need to know for the exam, so you just have make sure you get through all that. Citizenship is in the national curriculum so all children in England and Wales are meant to have it even if they are not taking it as a GCSE, but most schools don't have specialists and it tends to get covered very perfunctorily in form time and the like, just enough so if Ofsted challenged them they could tick the box.

Gordon Stainforth 01 Sep 2019
In reply to TobyA:

Personalised number plates. Many/most of which are frankly rather pathetic, even pitiful, and only very, very occasionally amusing. They raise a lot of questions, mostly rather awkward and/or embarrassing, and having implications that don't necessarily reflect too well on their owners (i.e., perhaps doing the opposite of what they were intended to do ... whatever that was...) Smiley, because I don't want to get too heavy about this, but they do seem a rather baffling waste of money to me.

Tom V 01 Sep 2019
In reply to Gordon Stainforth:

VIZ has the right term for them, Gordon:  tw*tplates.

I once got into a spot of bother by remarking to a young female colleague that I'd noticed she'd got a new set of tw*tplates. Turned out she wasn't a VIZ reader. 

marsbar 01 Sep 2019
In reply to Gordon Stainforth:

I think sometimes they are gifts.  

jkarran 01 Sep 2019
In reply to TobyA:

> So it's voltage that gets you, not current, in terms of electrocution? I do remember vaguely learning about this at school but it's a long time ago! Child #1 is doing really well in physics at school so if I can drag him away from computer games for a bit he'll probably explain it to me!

It's the current that hurts/kills but people are reasonably resistive so you need a high voltage to drive a killer current.

Think of your pan as a single turn transformer coil, the pan bottom is basically a washer shaped low value resistor with current flowing one way then the other thousands of times a second induced by a magnetically coupled coil below the glass, your pan is quite a good electrical conductor so no significant point to point voltage is developed as a result of the current induced in it.

V = I * R

I don't know how taxidermy works. 

Jk

jkarran 01 Sep 2019
In reply to Chris Craggs:

> The Med basin is filled to the lip of the Straights of Gib with warm saline water which spills over and sinks into the cold Atlantic eventually fanning out as a lens of hot salty water

In clear conditions you can see a haleocline as a rippling surface below the surface. It changes the refractive index to both light and sound making it useful for hiding submarines and piping sound hundreds of miles across oceans. It can also be used to store hot water under an insulating jacket of cool industrially, the salinity step breaks the convection cycle and without convection water is a pretty good insulator. 

Salt does weird things to water. 

Jk

Darren Jackson 01 Sep 2019
In reply to TobyA:

Why Wye?

Andy Hardy 02 Sep 2019
In reply to Gordon Stainforth:

I know one bloke who has tw@ plates on his car, but the reg. spells out part of his company name.

The other reason I have been given, is that if you buy a big posh car to impress your clients, you can keep it for longer because no one can tell it's (shock, horror) 5 years old. 

But I'm with you, I think they're tacky.

Tom V 02 Sep 2019
In reply to Andy Hardy:

Apart from being expressions of vanity they can bring out the worst in people walking by with a set of keys in their hand.

1
graeme jackson 02 Sep 2019
In reply to TobyA:

I don't understand how one can steal battery charge from someone else's mobile phone simply by putting them next to each other. Seems like witchcraft to me.

Dave Garnett 02 Sep 2019
In reply to TobyA:

I think I understand, at least in principle, how an induction hob works.

What I have demonstrated repeatedly is that I don't understand how to switch one on. 

Dave Garnett 02 Sep 2019
In reply to Gordon Stainforth:

> Personalised number plates. Many/most of which are frankly rather pathetic, even pitiful, and only very, very occasionally amusing.

I agree, although I think if they don't look obviously personalised and refer to something obscure but very relevant they can be amusing if you are in on the joke.  When I was working in the lab I occasionally thought it would be fun to have P56 LCK but (a) I wasn't the first to identify or clone this molecule and (b) I didn't have a suitably eccentric MGA or Morgan Aero to which to attach it . 

Gordon Stainforth 02 Sep 2019
In reply to Dave Garnett:

I agree (as I said before) that on the quite rare occasions that they amusing they are forgivable - on the simple grounds that they bring some entertainment to the world, i.e. contribute at least something and are so not a complete waste of money.

Tom V 02 Sep 2019
In reply to Gordon Stainforth:

I can only wonder what the 36 council workers in my area faced with job losses think about the mayor  of a Labour council swanning around in a limousine with a number plate worth six figures. 

Tom Last 02 Sep 2019
In reply to TobyA:

My head 

Blue Straggler 02 Sep 2019
In reply to graeme jackson:

> I don't understand how one can steal battery charge from someone else's mobile phone simply by putting them next to each other. Seems like witchcraft to me.

I don't understand how my iPhone slowly learns to reject non-Apple lightning charging cables.

Tyler 02 Sep 2019
In reply to TobyA:

I often ponder this. If I was transported back in time I don't think I would be able to impart anything useful that would help accelerate humanity out of the dark ages. I could describe all manner of wonderous technologies but if asked to help get them working I wouldn't even know where to start. In fact, I  wouldn'tv even be able to help move humanity into the iron age as I know nothing practical about mining or smelting; the wheel and fire is about as far as I go.

In short, I am Ark Fleet Ship B material.

Lusk 02 Sep 2019
In reply to Tom V:

> VIZ has the right term for them, Gordon:  tw*tplates.

> I once got into a spot of bother by remarking to a young female colleague that I'd noticed she'd got a new set of tw*tplates. Turned out she wasn't a VIZ reader. 


I must be developing dyslexia, because all private plates seem to read as 'Wanker' to me.

LastBoyScout 02 Sep 2019
In reply to Tom V:

> Yawning. Why is it infectious?

A yawn is an involuntary reflex to an oxygen deficit in the body. If you are bored or tired, your breathing will slow down which will cause you to take in less oxygen and so your body will trigger a yawn to help breathe in more.

It has also been suggested as a way of cooling the brain, as people yawn more during the summer than the winter. It is a way of increasing your heart rate blood flow and the use of muscles in the face which all help cool down the brain.

Can't find it at the moment, but I remember reading somewhere years ago that sympathetic yawning had something to do with the fact that if one person yawns, they push out a sudden blast of CO2, which triggers yawning in those nearby, due to the sudden localised drop in oxygen concentration, which seems to go along with the above, as they will have also first sucked in a load of O2.

However, it seems that there is also "contagious yawning", where you yawn due to just seeing or hearing someone else yawn, even if they aren't nearby - such as a picture or on film. It even works cross-species. Lots of complex theories for this - including such things as mirror neurons.

2
Toerag 02 Sep 2019
In reply to TobyA:

> I think this is the bit I need to get my head around to stop half expecting to get a shock when I pick up the coffee pot! ;-)

Voltage is what drives electrons to move, or to put it in a practical sense, jump a gap. To do this you need the voltage to be different between two points, one of which is often 'earth/ground'. The induction hob doesn't really induce much of a voltage in the pan, it's more a case of a magnetic effect making the metal atoms in the pan flip around repeatedly without actually moving anywhere. My analogy would be to get a bunch of schoolkids in the hall to run to the north and south ends of the room when you call out north or south.  If you call north-south-north-south repeatedly very fast they use a lot of energy by turning back and forth, going nowhere and turning it into heat. If you just called out one direction all the kids would end up at one side, this is like generating a voltage across the hall.  The induction hob creates a current without allowing the voltage to ramp up to a level where it jumps gaps.

Iron works well on induction hobs because it's very magnetic - the word coercivity springs to mind but I'm not entirely sure I'm correct.  Other metals will generate eddy currents, but they're much lower than the ones iron gets. for example, if you spin an aluminium disc at high RPM then bring a magnet close to the side of it, eddy currents will create a braking effect on the disc that increases with RPM.

> So it's voltage that gets you, not current, in terms of electrocution? I do remember vaguely learning about this at school but it's a long time ago! Child #1 is doing really well in physics at school so if I can drag him away from computer games for a bit he'll probably explain it to me!

Voltage is the gap jumper. So, you can put touch the ends of a 1.5v battery quite safely because the voltage isn't enough to cause the electrons to flow in your body. A lightning bolt at 1million volts can cause electrons to flow across a gap a mile wide to the clouds.  Current has a heating effect. when you shortcircuit a car battery with a spanner a massive current flows through it and it gets very hot even though it's only diven by 12V. So, voltage is what gets the elctricity into you but it's current that kills you when that electricity flows through you. The combination of the two is power - 1 amp of current at 12v is 12watts. 1 amp of current at 240V is 240W, twenty times the power.

Post edited at 18:28
Lusk 02 Sep 2019
In reply to Toerag:

I have an old neon lamp transformer that offers a generous 15,000 Volts (I think). Great for making miniature Jacob's Ladders with welding rods.
Completely safe to touch the electrodes because the Tx is current limited to something around 10mA.

Must rebuild it again sometime soon

Eric9Points 02 Sep 2019
In reply to Lusk:

Normal arc welding machines are the opposite. They use a low voltage, 105V IIRC and lots and lots of amps. Several hundreds sometimes. Safe because the voltage isn't high enough to push the amps through your body.

Lusk 02 Sep 2019
In reply to Eric9Points:

Thankfully we're slightly more resistive than a couple of pieces of metal

If anyone is particularly interested in electric shock, this is worth a read:
http://www.beama.org.uk/resourceLibrary/beama-rcd-handbook---guide-to-the-selection-and-application-of-rcds-.html

Dave Ferguson 02 Sep 2019
In reply to TobyA:

I don't understand my wife's shopping habit, particularly her penchant for sending almost half of the items back. I wish I understood, but 25 years on it remains a mystery.

WaterMonkey 02 Sep 2019
In reply to Lusk:

My party trick as a young electrical apprentice used to be to touch the live conductor of a 240v socket, ensuring I was stood on a carpet or in trainers and therefore not earthed!

1
Lusk 02 Sep 2019
In reply to WaterMonkey:

That reminds of possibly one of the dumbest things I've done in my life, and also highlights gross irresponsibility of behalf of my Professor graded lecturer ...
On his suggestion, impress people by taking a socket off and sticking the Neutral on your tongue whilst it's still powered up.
So, the numbnut that I am, gets home after a few beers, "Aye up Mrs, watch this".
Thankfully I had fault free wiring.

wintertree 02 Sep 2019
In reply to Lusk:

> On his suggestion, impress people by taking a socket off and sticking the Neutral on your tongue whilst it's still powered up.

I’d be worried about saliva making contact with the live side.  Especially after a brew or 3...

marsbar 02 Sep 2019
In reply to Lusk:

Common sense sometimes appears to be inversely proportional to qualification level.  We were subject to a long lecture on electrocution before being allowed to do practicals.  I also remember one of my lecturers totally ignoring the really quite sensible instructions regarding wedding rings and not sticking your hands in things involving 3 phases.  He got away with it.  I think that was when I realised that the people in charge don't always have a handle on the situation.   

wintertree 02 Sep 2019
In reply to marsbar:

>  I also remember one of my lecturers totally ignoring the really quite sensible instructions regarding wedding rings and not sticking your hands in things involving 3 phases.  He got away with it.

On that note, if you ever find yourself demonstrating the Leidenfrost effect by plunging your bare hand and arm into a dewar of liquid nitrogen, don’t forget to take any rings or watches off first...

Having followed several links from this forum on “degloving”, I fastidiously take my ring off before anything more advanced than dressing myself or reading a book.

Tom V 02 Sep 2019
In reply to WaterMonkey:

I know a bloke who hammers 6" nails up his nose. Still around as far as I know but apparently one sneeze will be curtains for him.

1
Rog Wilko 03 Sep 2019
In reply to Gordon Stainforth:

> I agree (as I said before) that on the quite rare occasions that they amusing they are forgivable - on the simple grounds that they bring some entertainment to the world, i.e. contribute at least something and are so not a complete waste of money.

Some of my favourites:

P15SED seen on a rather battered old Jag outside a pub near Alfreton

D161TAL on car belonging to a local tech company

And some I wish I'd seen:

MU51CAL for Lloyd Webber

PO11TAX for Thatcher

cb294 03 Sep 2019
In reply to LastBoyScout:

No one really knows why we yawn. Nevertheless, some explanations are obviously wrong, such as the face muscle/brain cooling link. This just does not work physiologically.

Also, CO2 exhaled during a yawn has no influence at all on the oxygen partial pressure, unless you directly exhale into someones nose. but that would not be different from a normal breath.

In any case, CO2 is sensed directly (or indirectly via pH), not via a drop in O2: If the air in a room full off people gets stuffy it is not because oxygen gets used up, but because CO2 levels increase! You open the windows to get rid of CO2, not to replenish O2.

None of this has anything to do with yawning. The heart rate increase you mention is more likely related to feedback from a sympathicus response, i.e. a yawn is, way back in evolution, probably related to a mouth open threat gesture (I am tired, better not disturb me...). Not particularly impressive in humans, but watch a hippo, dog, baboon or chimp yawn!

This would also easily explain why yawning is contagious.

Of course the recognition of a yawn must be encoded somewhere, but invoking mirror neurons looks like an attempt to make it sound sciency:

 "Supernormal Incremental Precipitation Inducer'. ... want to shove a `Quasi' in there somewhere to protect ourselves....."

CB

Hat Dude 03 Sep 2019
In reply to TobyA:

Why did the mushy peas with my F&C supper go cold so much faster than the rest?

Jack B 03 Sep 2019
In reply to Hat Dude:

Guessing here, but...

Mushy peas have a decent water content.  A small amount of the water will evaporate, and that will cool the remaining peas quite effectively.  The fish and the chips have less water and more fats/oils, which do not evaporate at these temperatures.

Or maybe its because you went to one of those weird places where they put the fish and chips together in a big pile, and the peas in a silly little Styrofoam cup. Then it's the square-cube law that gets you.

1
Hat Dude 03 Sep 2019
In reply to Jack B:

> Then it's the square-cube law that gets you.

Does this still apply if it's a round pot? ;-)

EddInaBox 03 Sep 2019
In reply to Hat Dude:

Depending on the distortion of space-time it may not be round at all.

Dave C 04 Sep 2019
In reply to Bob Kemp:

> I'd add most of quantum physics, astrophysics, nuclear physics etc.. Always fascinating, frequently incomprehensible...


For getting a grip on quantum mechanics, try John Gribbin's "Six Impossible Things", a fabulous little book that I found most helpful.

Toerag 04 Sep 2019
In reply to Hat Dude:

> Why did the mushy peas with my F&C supper go cold so much faster than the rest?


Because they're not really very hot to start with and the volume is low - the chippy keeps them in a bain-marie at <100degrees. The fried items come out the fryer at higher temperatures, and there's more volume of them thus take longer to cool down.

GrahamD 04 Sep 2019
In reply to Dave C:

> For getting a grip on quantum mechanics, try John Gribbin's "Six Impossible Things", a fabulous little book that I found most helpful.

I would suggest that if you now have a grip on quantum mechanics, you didn't understand what you were reading    possibly.

bouldery bits 04 Sep 2019
In reply to TobyA:

UKC.com 

n-stacey 04 Sep 2019
In reply to TobyA:

Why some members on here are so opinionated and think that they are so right!

Bob Kemp 04 Sep 2019
In reply to GrahamD:

> I would suggest that if you now have a grip on quantum mechanics, you didn't understand what you were reading    possibly.

Sounds about right, but I will take up Dave's suggestion. It seems as if no-one really knows what it's all about, but some people can do the maths. Found this in a review - 

"We’ve known that the world of quantum physics is strange for a century. But the distressing thing about this state of affairs is that we still don’t really know what’s going on." Oh well... I like to think there are still some mysteries in life. 

bouldery bits 04 Sep 2019
In reply to TobyA:

If there's a plane on a runway....

Blue Straggler 05 Sep 2019
In reply to Rog Wilko:

Robert Bourne and Sally Greene’s registration plates are pretty legendary, relevant and amusing, anyone who doesn’t smile at them must be a bitter old curmudgeon. 

Blue Straggler 05 Sep 2019
In reply to TobyA:

I didn’t previously understand why airports don’t have big clocks visible, but now I think I do. 

TobyA 05 Sep 2019
In reply to Blue Straggler:

> I didn’t previously understand why airports don’t have big clocks visible, but now I think I do. 

Why?

n-stacey 06 Sep 2019
In reply to Rog Wilko:

What about the Steve Parish reg, PEN1S.

n-stacey 06 Sep 2019
In reply to marsbar:

Is it to do with Sperm Whales?

n-stacey 06 Sep 2019
In reply to yeti:

"and ... why can you still think while being shot with a tazer, when all your muscles lock up?"

Lol.. Awesome..

Ardo 06 Sep 2019
In reply to n-stacey:

Not sure it was a private plate, as this was back in the day, but always chuckled when I saw GAY 50D driving around.

n-stacey 06 Sep 2019
In reply to Rog Wilko:

From what I have read in this post, there are quite a few authors on here who should have a special type of number plate which spells out 'self opinionated wanker'.

Just an observation.

Timmd 06 Sep 2019
In reply to TobyA:

I'd like to understand how some people manage to take more than a minute or so at the cash machine. 

Enter pin, pause, press more buttons, pause, view details, pause, ponder ponder, pause.... Aaaiieeee! What do they do?

It always seems to be when I'm in a rush...

Post edited at 14:50
wercat 06 Sep 2019
In reply to Timmd:

not everyone has good eyesight?

Timmd 06 Sep 2019
In reply to wercat:

Hmn, I'm feeling bad at being irritated now, that's a very good point. 

Blue Straggler 09 Sep 2019
In reply to Timmd:

> I'd like to understand how some people manage to take more than a minute or so at the cash machine. 

On DK.com (Deutsch Kletter) someone is writing the same thing, having been stuck behind me at German ATMs and railway station ticket machines 

i.e. maybe the people that irritated you, are from another country where the machines work differently 

Blue Straggler 09 Sep 2019
In reply to TobyA:

> Why?

Sorry, I’ve been slightly offline 

It’s to put the responsibility onto the passenger. A load of big clocks would make another crucial maintenance job. Imagine if one malfunctioned and it was 20 minutes until it could be corrected. People relying on that clock could miss their departure. Of course there is a time display on the electronic departure boards anyway, but those have to always be very well maintained. It’s possible (just speculating now) that maintenance of departure boards is subsidised by airlines but airport clocks would be the responsibility of the airport.

Also a big conspiracy to make you go for that impulse purchase of a £10k watch in the posh watch shop 

Timmd 09 Sep 2019
In reply to Blue Straggler:

> On DK.com (Deutsch Kletter) someone is writing the same thing, having been stuck behind me at German ATMs and railway station ticket machines 

> i.e. maybe the people that irritated you, are from another country where the machines work differently 

Very possibly. At least I amused a brother, by commenting that special 'hurry machines' should exist which give you your card back after 30 seconds to a minute's time, finished or not.  

Edit: While spaced out (and being left handed) I did what felt natural for me at a train ticket barrier recently and used my left hand - and reacted in surprise when the barrier to my left opened and I had to switch barriers. The ticket staff looked at me as if I was daft, I didn't quite have the mental energy to explain. It could seem that in many ways, things are designed so that anybody who is somehow different or challenged can end up wrong footed. 

Post edited at 21:03
krikoman 10 Sep 2019
In reply to TobyA:

Things you don't understand but wish you did..... Women

Hooo 10 Sep 2019
In reply to TobyA:

People!

Timmd 10 Sep 2019
In reply to krikoman:

> Things you don't understand but wish you did..... Women

It's occasionally occurred to me that most people are probably understandable if enough time is spent with them to gradually absorb their ways, even across the gender divide.

Post edited at 13:03
krikoman 10 Sep 2019
In reply to Timmd:

> It's occasionally occurred to me that most people are probably understandable if enough time is spent with them to gradually absorb their ways, even across the gender divide.


You haven't met some of my ex-girlfriends

As an example, I once got into an argument with an ex, because I wasn't angry enough about someone else forgetting their key, which made us have to drive 20 minutes out of our way, on a four hour journey!!

Mind you, I don't understand some of my male friends either, I suspect this is reciprocal.

Post edited at 13:06
Timmd 10 Sep 2019
In reply to krikoman:

Ha ha, I'm not saying that some people aren't just bonkers nut, humans 'who feel sane' can be a blessed discovery. 

A sister in law once said something wise to me, about how a big lesson for her was not expecting other people to react like her, respond to things like she would do. She thinks we all get weirder as we get older too - that's possibly people refusing to assimilate as much as when they're younger. 

I have a lifelong male friend who still has me furrowing my brows rather a lot. 

Post edited at 13:51
Blue Straggler 11 Sep 2019
In reply to Blue Straggler:

> i.e. maybe the people that irritated you, are from another country where the machines work differently 

To elaborate slightly on this, I have also found that Deutsche Bahn ticket machines seem to operate differently according to city


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