Made for each other: liquid nitrogen and 1,500 ping-pong balls It's the rare scientific mind that has the pure intellectual chutzpah to tackle a problem that has troubled boffinry since the discovery of cryogenics – namely, "What happens if you combine liquid nitrogen with 1,500 ping-pong balls?" C'mon, don't tell The Reg that question hasn't crossed your mind. It hasn't? Well, then you …
This trick is very very old one for folks trained in the field of Low Temperature Physics. I remember seeing this done in the 1970's while in graduate school, and the person who did it was in his 60's and claimed to have first seen it when he was in graduate school.
More. Look carefully at the audience. Zoom into fullscreen if you have to. You will see that these are not the 9k paying students you are looking for.
This looks like a circus run for the entertainment of candidate foreign students during an open day tour. If memory serves me right you are allowed to charge these more than the base 9k fee which locals have to pay.
The kids paying the £9k/year (that a lot of these kids still don't seem to have realised they only pay back long AFTER they use the service) who get the direct benefit of the education and increased lifetime financial earnings makes more sense to me than a cleaner on £15k/year struggling to make ends meet paying their £9k for them.
Sure, if you want 10% of the population to go to Uni society can afford it. At 50%, it's not sustainable, and those who benefit should pay more of a contribution.
I'm sorry if I can't bring myself to weep for these kids.
No, you can't bring yourself to weep for these kids. You're rich enough for your kids to be able to go whaterver the fee and it's the only the plebs and chavs that will be put off going by the 9 grand a year price tag.
An educated workforce obviously does nothing for the economy as a whole, and the last thing we need is a group of working class oiks getting above themselves because they have an "education"....
The way these new rules actually work means that many of them will never actually pay back as much as I will, as I was under the original Labour rules which were "You WILL pay the whole lot back unless you die first. And no, you still owe us the money even if you're bankrupt."
Thus the boundaries and repayment rates meant that some student would be paying the interest on the student loan for their entire life.
It got changed a couple of years later to "We'll write off the remainder after 25 years", but the boundaries still meant that many would pay back more than the original loan amount.
The new rules are writing off after 30 years, but now the boundaries are such that the national average pays back £33k total on a loan of £27k, and most of those below average earnings will have paid back less than they borrowed before the write-off.*
So how exactly does that loan put them off?
Unless of course it's because they can't do the maths, in which case they probably shouldn't be doing a science, maths or engineering degree anyway, so job done at promoting those!
* Source: BBC Student Finance
Yep, just been working this out myself. For each student that doesn't become a "high earner", i.e. 60K (*) plus before they are 40, the government (thats us) will end up spending more than they (we) would by paying the fees up-front. Mind you the private companies involved will do quite well out of it, so thats nice.
(*) excl inflation
Already happening at my work place. They come straight out of Uni and end up same place I am working as there isn't any other jobs. But once here they seem to think they are better because they have a bit of paper, I make sure I put them back in their place quick smart. Not only are they lazy and weak but can't even do basic problem solving on the job. People must realise we can't all be doctors otherwise everything we have in society will crumble. Uni is just a sham to take people's money and keep it looking like governments are doing something. What is the bet there will probably be uni degrees for cleaning sooner or later! Laugh all you like now but there are already uni courses for topics that clearly don't need it.
Here is just a sample of some of the most rediculous, But there are many many others.
http://www.toptenz.net/to-10-useless-college-classes-degrees.php
The problem with your argument is how you go from 50% to 10%. You seem to think that the way to restrict the numbers is to make sure that only the rich can afford to go to university. I would argue that it's more important to encourage the less well off to get a degree, as their prospects are often worse.
" You seem to think that the way to restrict the numbers is to make sure that only the rich can afford to go to university."
I feel I have to butt in here and say that didn't get that sentiment from the OP. On the contrary, they seemed to be bemoaning the fact that we had gone from 10 to 50 and *as a consequence* had to ditch the previous system.
just my 2p worth....
It used to anoy the hell out of me that in the past, when kids who's parents were on low incomes and all the tuition fees were paid for by the state and recived grants to live on for the time they were at uni, only to piss off overseas and take on well paid jobs and not paying uk tax repaying the investment the state made in them.....
with student loans, at least they are investing in their own futures.
The student loan system will if anything stop the masses of people doing nonsense courses that never leave to a job, but they see it as better than getting a job in the first place.
If anything, I think the state should write off a % of the loan for each year they are paying tax in the UK so that people can be out of debt for their studies sooner.
It does not bother me or my daughter that she is likely to be 40k+in debt by the time she finishes uni. she will be well qualified as a dentist and be earning more than that each year
I would have thought that the most scholastically gifted would be the best ones to go through University.
It should have nothing to do with how rich daddy is.
Having a bunch of rich knuckleheads coasting through a soft arts degree on daddies dollar is no better or worse than having a bunch of poor knuckleheads coasting through a soft arts degree on the taxpayers dollar, except for the fact that I don't have to pay for daddies little princess I guess.
What you need to do is educated everyone to a level, then subsides University courses that produce graduates in a needed fields.
i.e. take medicine or engineering and the course is free - take media studies, sport science or drama charge £15k a year. Then when you have enough engineers and doctors start raising the fees. But the chances are you'll never have enough doctors an engineers; the rich will still send their kids to University to do History and modern art but we wont be subsiding muppet's who are just putting off working in a call center for another 3-4 years so they can piss it up.
"Sure, if you want 10% of the population to go to Uni society can afford it. At 50%, it's not sustainable, and those who benefit should pay more of a contribution."
I'd rather we as taxpayers paid for that 10% to go to university assuming that they go on merit alone (which I'd admit is hard to enforce). The current system of churning out tens of thousands of rubbish graduates that can barely spell their own names and have zero interest in their subjects is no use.
While I do think that learning should not be dreary, and neither accompanied by whipping and memorizing, I also am unconvinced that a 5 minute-stunt at an expense, even a relatively low one, is anything but a stunt, a marketing exercise by this good university.
Instruction this is not. Explanations given immediately before, seemingly to unprepared students, no calculation done. Is this the tertiary education of the nouveau rich; entertainment to get them kids off their iPhone5 for some minutes with a bang? Silly laughter, exit, and the assistants cleaning the floor nicely from glass debris and collecting 1500 ping-pong balls. Thank you.
Lets see some of what the experiment demonstrated:
Liquid / gas transition. materials strength, thermodynamics, Newtonian physics and much more.
That one demonstration can provide hours of lectures across multiple fields. Instead of dreary diagrams trying to get a point across they can refer directly to the demonstration, something that the students will vividly remember and something that takes it out of the realms of classroom theory into a real world example.
You are also confusing laboratory work with a demonstration. If this was laboratory work then the students themselves would be setting up the experiment and the instruments to take the measurements. Thinking about it, there's another lecture for you. He can ask the students how they would set it up as an experiment, what they would measure and how, what it would tell them etc...
It is pity that your lack of imagination and your obvious prejudices limit you so much.
There are some studies that point out that the dreary approach (rote memorization and lengthy practice drills) actually yields better long-term results. I don't know why, but I think it's because that combined with a very high competitive bar (I think they were comparing Japan in this case, which tends to foster mutual competition) tends to make the students focus, and focused learning tends to stick better because there's a motivation behind it..
I think you'll find it is useful in demonstrating the amount of force that can be generated by a liquid evaporating (albeit one that does so at -196C). Most would not have realised that this level could occur from such a small amount of liquid. That bin bounces a long way up.
Perhaps you don't know of the Purdue University "Light a barbecue with liquid oxygen" video which went viral on the early public Internet? It's said it significantly increased applicants for science courses at Purdue. This is a good example of low-cost marketing. True. But whoever said that universities don't need to do it?
I went to completely the wrong university for what I wanted to do (Cambridge, as it happened) because in my day there was too little information about different universities and different courses. With so much information nowadays, stunts like this may cause students to read up on a university they would not otherwise have considered, that may be better suited to their interests and needs. So don't knock it.
Learning how to learn is the most important lesson, sometimes you can do this with a bang rather than a book, if everybody was the same then teachers would only need to teach one way.
We are not all the same, this experiment may well have enthralled one student enough to study physics, if this is the case that's *enough* to make the whole exercise it, maybe it's those cool things which excites people enough to ask "what if".
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Not in our classes they weren't. One of the chemistry teachers was fond of making water by lighting balloons filled with a 2:1 mixture of hydrogen and oxygen. Used to wake up those sleeping through maths in the classrooms below the lab.
We had accidental ones too though. Mine involved a probable toluene residue from the previous day in a test tube used for a nitration experiment. Oops :)
This stuff has a long history. I have a 1910 chemistry textbook which describes and experiment in which a long lead tube is filled with a mixture of carbon monoxide and oxygen. At one end is a boiling tube in a large shield. The other end is sealed and a spark generated. Of course it has a serious purpose: to show the speed of flame propagation in a gas/oxygen mixture. The reduction of the boiling tube to sand grains is just a little added flourish.
I was wondering about that myself.
The reaction from the explosion shoves the nitrogen and the balls out and up; that ought to push the bin down. I hypothesise flex in the bottom of the bin, but I'm not at all certain if that adequately explains it. Another thought is that there is a mechanical coupling between the balls and the bin, or perhaps a hole is blown in the bottom of the bin.
I would guess that as the Nitrogen returning to a gas expands and, its weight at a given volume and pressure reduces. Having disposed of the rest of the contents of the bin in the expansion, perhaps the bin becomes lighter than air and floats for a brief second before mixing with air and sinking.
But then, I'm just an IT bod..
There's a vacuum involved. There is no vacuum here.
Seems rather more likely to me that the force of the explosion pushes the centre of the base of the bin outwards by a small amount; enough to impart an upwards motion to the rest of the bin. I doubt the floor is elastic enough to provide sufficient force if the bin itself is totally rigid.
A similar experiment (preferably one with a more powerful boom) in a metal bin might help demonstrate this in a fittingly graphic manner.
These are lessons those guys will remember, not the sat in a classroom going through dreary powerpoints or sat doing calculations. The lessons I remember from school are things like this. Magnesium + iodine, burning through an asbestos mat into the school long jump pit was one I really remember. Barely remember any of my computing lessons though even though that is my field.
Oh and I suspect this was a lesson given to school kids not university students, in order to encourage them to go to university.
Francium in water is my science memory from school. :-)
Oh, someone had to make me fetch the grumpy pedant hat.
You did not see francium in water at school. No-one will have seen francium in water anywhere. No-one has even seen macroscopic quantities of francium, even in a research lab. You will perhaps have seen videos of caesium or rubidium in water, and probably have seen potassium and sodium in water first hand.
I won't down vote your for it as it's probably just misrememberd, but francium is so astoundingly rare no teacher would have it, let alone just to chuck it in some water for the kids, it's also very radioactive (with a short half life).
If it was enthusiatic, it was probably potassium.
Thermite demo on the front bench resulting in droplets of molten iron being embedded in the chemistry lab ceiling is the one that sticks in my mind...
Here's another liquid nitrogen/water/dustbin experiment, this time with rubber ducks:
http://www.wired.com/wiredscience/2012/05/exploding-liquid-nitrogen-where-does-the-energy-come-from/
...The lessons I remember from school are things like this. Magnesium + iodine, burning through an asbestos mat into the school long jump pit was one I really remember...
I also remember big fun with sticks of magnesium in high school. An experiment called for it, and the teacher brought it in, packed in gel in metal casks, explaining why this was necessary to keep the magnesium from contacting air or water until ready, telling us the story of what happened to a kid who tried to sneak some out in his pants pocket.
It wasn't two hours later that a loud bang was heard echoing from a boys' bathroom in the science wing, quickly followed by a teacher's voice shouting "come back here, you!"
Oh and I suspect this was a lesson given to school kids not university students, in order to encourage them to go to university.
This is possibly the most entertaining use of ping-pong balls in the name of science since I saw that old Disney movie Our Friend, The Atom in the third grade.
A cold one for the professor.
"also remember big fun with sticks of magnesium in high school. An experiment called for it, and the teacher brought it in, packed in gel in metal casks, explaining why this was necessary to keep the magnesium from contacting air or water until ready, telling us the story of what happened to a kid who tried to sneak some out in his pants pocket."
Not magnesium.
Sodium, potassium or lithium probably.
The talk I went to the Uni for (while still at school) involved a lecturer telling us that he's not allowed to buy liquid oxygen, so he produces his own, setting fire to digestive biscuits dipped in oxygen whizzing around like catherine wheels.
In chemistry we made cordite, different types of thermite (one from plaster), fuming nitric acid, iodoform, it put things in context, made me ask "why?" and boring things (like charge on the electron) became part of the big puzzle, an became interesting.
I was lucky to attend one of Dr John Salthouse's lectures at Salford Uni in 98. He's been described as a pyromanic with a chemistry degree and I'd concur. Even my school's department head was in awe and he was also a pyro (and the my school left one lab unrefurbished for him, on the basis of it having survived that teachers experiments since the 60s, it would carry on - notably a 3rd floor room, with windows on 3 sides and it's own fire escape)
I'm not saying some of the bangs were loud, but we were in the biggest lecture theatre at Salford's chem dept, and one bang broke a ceiling tile and dropped it (right at the back, up the aisle from the bang, clearly an acoustic concentration with the aisle funneling and the back wall echo) an impressive feat I'm sure you'll agree. Sometimes I wonder if I should have done Chemistry, instead of Robotics as my degree subject....
Ah yes, I came here to reminisce about Dr Salthouse also, having enjoyed a lecture of his circa 1987 (?) when he visited our secondary school and did various hairy things with liquid oxygen, oxyacetylene, hydrogen, digestive biscuits etc. Standard test for hydrogen being a squeaky pop from the test tube? Not when the test tube is six foot tall. Yes, we did have to break all safety regulations with the smoke alarms in our lecture theatre...
I was left unattended with some dry ice and a drinks bottle and made the same "experiment" minus the ping pong balls. I'd hypothesised the lid would would pop off and the sink would fill with cold water vapour. The bottle was placed in the sink wrapped with a wet cloth to warm it and catch the lid. The top of the sink was covered by a ceiling tile "just in case"...
A few minutes later it hadn't gone off and I was treating it like a lit firework and ignoring it. There was a very loud pop, cloud of ceiling tile and some water vapour...but no sign of the bottle. It had shot straight up, turned the first tile to dust and left a perfect bottle shaped hole in the ceiling above. Don't try this at home.
This is almost what happened with my first attempt at home beer making. Very stupidly, I put the half-fermented mixture into a glass bottle, put on the cap, and left it on a shelf in the garage (I was 15 at the time).
A few days later there was a loud bang. On investigating, the base of the bottle had sheared off, causing the bottle to be sent vertically into the shelf above, which was only thin plywood and now had a bottle wedged half way through it.
Isn't this vaguely the kind of thing that the late Oxford professor Nick Kurti (1908-1998) used to do, except (1) a lot of his experiments were edible (2) they were before the days of t'Internet and cameraphones (which is a shame).
What's Oxford for these days, besides PPE and fund-raising?
"Prone to blow stuff up.""
or
"Demos regularly exceed sound barrier in open air."
Seriously this teaches many valuable lessons. Especially.
1) Stuff does not work like a text book (the dustbin shouldn't jump, but it does). A *very* useful lesson to learn in our modern theory heavy, computer simulation loving world.
2) This stuff can be dangerous *unless* you take precautions. It might technically be a demonstration of rapid expansion through flash boiling but it looks *remarkably* like an explosion.
People usually decide to get into something because they see something and think "I want to be able to do that." All STEM education could do with a bit more of this.
1) The dustbin jumped because most dustbins that size aren't flat or rigid at the bottom. They usually have a recess down there to reduce friction when you have to drag it. When the nitro blew, contained even momentarily by the ping pong balls, the pressure probably inflated the recess down there, causing it to push down and strike the floor at velocity, working like a downward-striking piston.
2) A lot of things look remarkably like an explosion. Rapid combustion, for example. Explosion is a pretty vague term usually.
"1) The dustbin jumped because most dustbins that size aren't flat or rigid at the bottom. They usually have a recess down there to reduce friction when you have to drag it. When the nitro blew, contained even momentarily by the ping pong balls, the pressure probably inflated the recess down there, causing it to push down and strike the floor at velocity, working like a downward-striking piston."
Highly *probable*. For proper science you'd need to devise experiments that prove or disprove the hypothesis. Which is also what a good demonstration is all about.
"2) A lot of things look remarkably like an explosion. Rapid combustion, for example. Explosion is a pretty vague term usually."
http://en.wikipedia.org/wiki/Deflagration_to_detonation_transition
(Not got the time to dig out my standard textbook on this).
As you will see the correct term is "detonation" and it's *qualitatively* different (> Mach 1 pressure effect Vs typically 10s of ms^-1 chemical) from combustion.
A point which would probably be academic if you found yourself *inside* such a cloud.
Well, a good working definition of an explosion is "any rapid process, the final products of which take up significantly more space than the initial ingredients".
Quickly heating a lot of liquid nitrogen above its boiling point inside a closed vessel made of a (now) brittle substance definitely qualifies under this definition.
As an ex-chemist with training in the industry (not university) I was shocked by the lackadasial handling of safety measures:
1. Liquid nitrogen is handled with unprotected hands, although there are some heavy duty gloves lying on the table. When the professor removed the funnel he nearly did have an accident.
2. No safety glasses worn by him or his assistents where liquid nitrogen and an explosion are involved.
3. No protective clothing to protect his body, especially his naked arms under a short-sleeved shirt.
Sad state of "teaching by example" in the universities.
Personally, I avoid cuffs when handling liquid nitrogen as I don't want drops caught between cuff and wrist. The odd small drop falling on my hand just boils off, getting a drop squashed under clothing causes a cold burn. I used to actually roll my sleeves up when pouring from dewar into thermos. I suppose you could cover up completely.
Agree with funnel handling, those gloves should have been used, and agree with the safety specs - especially if there is liquid gas hanging about in open thermos flasks
I dare say you're one of those who require kids playing conkers to wear safety glasses and god help any circus performers... hard hat and safety boots before you get on the high wire...
Someone showed me his big vat of nitrogen then stuck his hand in it to demonstrate that the instantly vapourised liquid formed an insulating layer of gaseous nitrogen around his hand so it emerged unscathed. I hasten to add it was a very brief immersion and, despite understanding the physics and despite having had a demonstration, I declined to try the same trick.
Some questions to think about:
Prior to the experiment:
1. What is the expected distribution of balls after the event has concluded?
2. Which conservation laws to you expect to be relevant to the outcome?
a. Momentum
b. Energy
c. Entropy
d. GDP
e. Other
Explain your answer.
After the experiment:
3. If each of the balls had the name of a different observer written upon it, and afterward they were randomly distributed among the observers, what is the expected number of balls to be matched with their mate?
4. Describe the observed motion of the trash can and attempt to explain it in terms of the forces applied to it during the experiment.
5. How can the total energy release during the experiment be estimated by the distribution of balls once stability was achieved?
6. How might the end result have differed had the lid be place loosely upon the trash can?
7. List 4 ways energy was released and distributed from the hot water to the other physical components of the experiment.
GDP? I fail to see how one instance of this experiment would affect the country's Gross Domestic Product - unless you are counting the number of foreign students attacted to study in British Universities as a profit to the country. In my experience, many of the best of them go back to where they live and set up rival industries to ours.
This type of experiments is entertaining and conducive to science education whereas it may entails considerable environment deterioration or resouce dissipation. Hope people will correlate a experiment with some certain more tangible objectives other than pure entertainment or reduce its scale.
I don't think it would have cost that much to do, and if getting a bunch of people interested in science, or engaged with the subject they are being taught (because as this thread proves there's plenty of physics and chemistry to debate about around this demo) to an overall improvement is the end result then its money well spent.
"considerable environment deterioration or resouce dissipation" - are you kidding? Celluloid ping-pong balls and a few hundred millilitres of liquid condensed out of the air? Wouldn't surprise me if the balls were salvage from the sports centre, and liquid N2 is pennies per litre if you buy in significant quantities. The total environmental impact is probably equivalent to a couple of Big Mac Meals.
I remember going to an evening event that revolved around a big flask of liquid nitrogent - think it was organised by the local science teachers or something. A hundred or so pimply of us tweenagers fascinated for several hours by a beardy loon doing all the usual cryogenic tricks including turning whisky into syrup. I think it cost us about 50p each for use the school minibus to get us there.
The subject involved is not this case in particular. Some instances of this type of experiments may be less controversial. Pay attention to the number of 56649 in the following sentence excerpted from the penultimate paragraph of the article. "He has also roasted jelly babies in the name of science, and set the world's record for near-simultaneous fireworks-rocket launches: 56,649."
Meanwhile, recycling those ping-pong balls should be time-demanding.
It's great fun :) pop some crushed ice in a bottle, shove the bottle in a tub of water and kaboom!
Whilst at university, I came across liquid nitrogen once. A lecturer had only managed to cover about 2/3rds of the course he'd set, and rather than try and cover some of it in the last lecture of term he brought in a tin of nitrogen and froze a couple of bananas. I wasn't convinced that it was an entirely good use of time or money and it wasn't even that fun.
This is a great way of showing the dangers of handling liquid nitrogen. I know a story where a home thermos was used for holding liquid nitrogen (never use a non-approved container). Even the persons knew how to handle this gas, the lid was accidentally closed tight enough to cause pressure buildup. Extremely lucky enough, for the individual, he suffered injury which was not permenent. It could have been much worse.
There was a story at Hull Uni about a large dewar of liquid nitrogen that was left in a lab - one day someone noticed that the neck had frosted over. Panic ensued, the dewar was carefully dragged out onto a sports field and the TA took shots at it. in an attempt to reduce the pressure.
Turned out to be emptty.
(Story probably bollocks).
Probably - you *never* plug the top of a liquid nitrogen dewar. On the other hand, if you have liquid nitrogen standing around for long enough for it to turn blue, then you need to dispose of it ASAACAP: (clue, it's how Salthouse makes his liquid oxygen)....
(definitely safety glasses for this one!)
The old alma-mater.
Last news I heard from those guys was the business school getting a media roasting for their degree course in perfumery which required completion of a smell test as an entry requirement.
Good to see them getting better press for blowing stuff up.
I wonder if they managed to sort out that concrete cancer on the Babbage building.
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