MarkW Posted April 3, 2016 Share Posted April 3, 2016 OK, it's Sunday night and drink has been taken, so this might appear more straightforward in the cold light of day, but...Does a SCUBA tank filled with helium get lighter or heavier as you empty it? Quote Link to comment Share on other sites More sharing options...
Joeman Posted April 3, 2016 Share Posted April 3, 2016 Tank will never actually be empty - it will stop providing helium when the pressure inside matches the pressure outside.Full tank with helium under pressure will be heavier than a depleted tank with helium at atmospheric pressure. Quote Link to comment Share on other sites More sharing options...
MarkW Posted April 4, 2016 Author Share Posted April 4, 2016 Yeah, that's what I said: it would be heavier with 1 atm of air in than 1 atm if helium, but as helium also has mass the more you squeeze into the tank the heavier it would get. But then they started talking some weird gas-law physics shite and made my brain hurt. Quote Link to comment Share on other sites More sharing options...
XmisterIS Posted April 4, 2016 Share Posted April 4, 2016 I imagine they were talking about Dalton's law of partial pressures, or perhaps they were alluding to Boyle's law, but the overall mass of the cylinder is directly (not inversely) proportional to the pressure of the contents. Quote Link to comment Share on other sites More sharing options...
MarkW Posted April 4, 2016 Author Share Posted April 4, 2016 The gist of their argument was that if you had an unburstable balloon of fixed dimensions (let's say 1 litre) and replaced the litre of air with a litre of helium it would become lighter than air and float. But the more you squeezed in the heavier it would become as the mass of the pressurized helium exceeded the mass of a litre of air at 1 atm, and eventually it would sink. If you then let the helium out slowly the balloon would first become lighter and rise, then heavier and fall. Quote Link to comment Share on other sites More sharing options...
Joeman Posted April 4, 2016 Share Posted April 4, 2016 The gist of their argument was that if you had an unburstable balloon of fixed dimensions (let's say 1 litre) and replaced the litre of air with a litre of helium it would become lighter than air and float. But the more you squeezed in the heavier it would become as the mass of the pressurized helium exceeded the mass of a litre of air at 1 atm, and eventually it would sink. If you then let the helium out slowly the balloon would first become lighter and rise, then heavier and fall.Not necessarily.If the balloon is fixed dimensions, what's going to push out the remaining helium?Baloons deflate because the atmosphere squashes them down. If it's fixed at 1litre, you'll be left with one litre of helium at one atmosphere pressure. Quote Link to comment Share on other sites More sharing options...
soll Posted April 4, 2016 Share Posted April 4, 2016 gas works wierd, the more you compress it the denser it becomes, the denser it become the more liquid it becomes.there for a 1 litre cylinder can actually hold several litres of helium under pressure. so your friend answer is subjective... what is the compression ratio and what is the atmospheric pressure of operation Quote Link to comment Share on other sites More sharing options...
Fozzie Posted April 4, 2016 Share Posted April 4, 2016 This question sounds like a more complicated version of:What's heavier? A ton of feathers, or a ton of stone? Quote Link to comment Share on other sites More sharing options...
MarkW Posted April 4, 2016 Author Share Posted April 4, 2016 This question sounds like a more complicated version of:What's heavier? A ton of feathers, or a ton of stone? But how about a ton of gold and a ton of stone? Quote Link to comment Share on other sites More sharing options...
Hoggs Posted April 4, 2016 Share Posted April 4, 2016 ooh ooh how about a ton of lead vs a tonne of lead Quote Link to comment Share on other sites More sharing options...
XmisterIS Posted April 4, 2016 Share Posted April 4, 2016 (edited) This question sounds like a more complicated version of:What's heavier? A ton of feathers, or a ton of stone? There's something in Newtonian physics called the law of conservation of mass, i.e. matter cannot be created or destroyed (except it can, but for the purposes of this discussion it can't). Therefore it doesn't matter how many balloons you have, filled with helium, or feathers, or lead, or more balloons, compressed by hippos or spherical horses in a vacuum, matter (and therefore mass) cannot be created or destroyed.Nevertheless, if the total density of the baloon + helium (i.e. weighted average of density of balloon and density of contained gas) is less than the surrounding air, the balloon will float. Otherwise it will sink. (Ask Archimedes about that one!) Edited April 4, 2016 by XmisterIS Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted April 4, 2016 Share Posted April 4, 2016 ooh ooh how about a ton of lead vs a tonne of lead a tonne of lead is heavier than a ton of lead as a ton is only 0.90718474 of a tonne but i would not like to try and catch either of them if they were falling Quote Link to comment Share on other sites More sharing options...
Fozzie Posted April 4, 2016 Share Posted April 4, 2016 ooh ooh how about a ton of lead vs a tonne of lead A tonne of lead is just over 200 pounds heavier than a ton of lead... Blasted Americans always underestimating their weight!Incidentally... After having a cheat day of chocolate pancakes, chocolate, pizza, doughballs, beer and more chocolate, topped off with a chocolate cake. I am also 200 pounds heavier than yesterday. Quote Link to comment Share on other sites More sharing options...
MarkW Posted April 4, 2016 Author Share Posted April 4, 2016 ooh ooh how about a ton of lead vs a tonne of lead a tonne of lead is heavier than a ton of lead as a ton is only 0.90718474 of a tonne but i would not like to try and catch either of them if they were fallingIt's the ton of gold vs ton of stone one that catches people out: whilst most things in Imperial are weighed in avoirdupois (2,240 pounds in a ton) gold is weighed in Troy (2,430 pounds in a ton). So a ton of gold and a ton of almost anything else don't weigh the same. Unless it's a Metric tonne... Quote Link to comment Share on other sites More sharing options...
Hoggs Posted April 4, 2016 Share Posted April 4, 2016 I had a feeling gold was weighed in different terms but couldn't remember if it was less or more! Stupid things sounding the same but not Quote Link to comment Share on other sites More sharing options...
RantMachine Posted April 4, 2016 Share Posted April 4, 2016 We're missing the all important one, 7268 curly wurlys or a 2003 Fazer 600? Quote Link to comment Share on other sites More sharing options...
Stu Posted April 4, 2016 Share Posted April 4, 2016 We're missing the all important one, 7268 curly wurlys or a 2003 Fazer 600? depends how many I can eat before they are weighed Quote Link to comment Share on other sites More sharing options...
Hoggs Posted April 4, 2016 Share Posted April 4, 2016 We're missing the all important one, 7268 curly wurlys or a 2003 Fazer 600? OOH I love these...Hmm I reckon curly wurlys clock in at 188.968kg and the Fazer at 189 kg... but not sure if my figures include wrappers..... Also the fazer is dry weight. Wet weight is 205kgs so a clean winner Quote Link to comment Share on other sites More sharing options...
RantMachine Posted April 4, 2016 Share Posted April 4, 2016 Okay then, let's swap the Fazer for a Bandit 600 from the same year, and up the number of Curly Wurlys to 8000.Anyone know just how heavy the burden of shame really is? Quote Link to comment Share on other sites More sharing options...
MarkW Posted April 4, 2016 Author Share Posted April 4, 2016 More importantly still: If I go to the gym and get on the treadmill at 11 kph, how slowly would I have to eat a Curly Wurly in order not to put on any weight? Quote Link to comment Share on other sites More sharing options...
Hoggs Posted April 4, 2016 Share Posted April 4, 2016 Anyone know just how heavy the burden of shame really is? Where's Glorian when you actually need him? Quote Link to comment Share on other sites More sharing options...
iangaryprice Posted April 4, 2016 Share Posted April 4, 2016 Getting back to the original question.Does a SCUBA tank filled with helium get lighter or heavier as you empty it?It gets lighter as it empties.A typical 12liter scuba cylinder weighs about 12kg.Normally they are filled with air to 232bar, 12x232 = 2784litres of air.Density of air is 1.225 kg/m3 (1.225 kg /1000litres)Hence the cylinder contains 1.225x2784 = 3.41 kg.Hence empty cylinder 12kgFull cylinder 15.41kg.Helium density is 0.916kg/m3 (0.916kg/1000litres)Hence the cylinder contains 0.916x2784 = 2.55 kg.Hence full cylinder weight is 14.55kgSo you can see full cylinder 14.55kg, let air out and it gets lighter until 12kg when empty.The difference in weight between an unpressurised cylinder of air and helium is tiny its about 4g. Quote Link to comment Share on other sites More sharing options...
Bonniebird Posted April 4, 2016 Share Posted April 4, 2016 Glad there was an answerHowever............ compressed by hippos Made me lol. Don't really know why except its been a long day back at work after a week off Quote Link to comment Share on other sites More sharing options...
Joeman Posted April 4, 2016 Share Posted April 4, 2016 Getting back to the original question.Does a SCUBA tank filled with helium get lighter or heavier as you empty it?It gets lighter as it empties.A typical 12liter scuba cylinder weighs about 12kg.Normally they are filled with air to 232bar, 12x232 = 2784litres of air.Density of air is 1.225 kg/m3 (1.225 kg /1000litres)Hence the cylinder contains 1.225x2784 = 3.41 kg.Hence empty cylinder 12kgFull cylinder 15.41kg.Helium density is 0.916kg/m3 (0.916kg/1000litres)Hence the cylinder contains 0.916x2784 = 2.55 kg.Hence full cylinder weight is 14.55kgSo you can see full cylinder 14.55kg, let air out and it gets lighter until 12kg when empty.The difference in weight between an unpressurised cylinder of air and helium is tiny its about 4g. Not quite. Empty cylinder that contained air weighs 12kg. However that still has air inside - it's not a vacuum.So an empty cylinder that contained helium, will still contain helium. So and empty helium cylinder must weigh less than an empty air cylinder. Quote Link to comment Share on other sites More sharing options...
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