george_seamons Posted January 8, 2012 Report Share Posted January 8, 2012 I was at the cinema the other week with my girlfriend and another couple. We got some pick and mix sweets, and went to weigh them on the scales to pay. The (ripoff!) price came up, we paid, and off we went to watch the film. Whilst we were waiting for the film to start, the other couple asked the question (or moreso, made the statement) that "Putting a helium balloon in the pick and mix bag would make the final price cheaper, because helium weighs less than air". Now, I believed (and still do!), that this is a daft statement. They couldn't appreciate that adding the helium balloon to the pick and mix bag would make the bag weigh more than it did without the balloon being in there at all (because you have the weight of the actual balloon itself). However, they were insistent that it would be cheaper, due to the helium making the bag lift off the scales ever so slightly due to the effect of the helium balloon. So...who is right?! Quote Link to comment Share on other sites More sharing options...
ellingtj Posted January 8, 2012 Report Share Posted January 8, 2012 (edited) They're right, assuming the said ballon actually had the ability to float and the scales aren't in a vacuum. Think of it like this, the baloon will have lift or a force in the upwards direction, the sweets act downwards so the net downward force will be decreased by the baloon's presence. Edited January 8, 2012 by ellingtj 1 Quote Link to comment Share on other sites More sharing options...
Muel Posted January 8, 2012 Report Share Posted January 8, 2012 The weight of the balloon is irrelevant, the lift provided by the gas lifts the weight of the balloon, plus a bit more (otherwise it wouldn't tug your hand and try to fly away). Depends how much helium you you though. Quote Link to comment Share on other sites More sharing options...
tomturd Posted January 8, 2012 Report Share Posted January 8, 2012 If you scale the ballon up to the size of a weather balloon or something (just for arguments sake), then it wouldn't even sit on the scales. Quote Link to comment Share on other sites More sharing options...
george_seamons Posted January 8, 2012 Author Report Share Posted January 8, 2012 ...but then the cost of the helium outweighs the cost of the pick and mix I guess its all relative to the size of the balloon. Quote Link to comment Share on other sites More sharing options...
ogre Posted January 8, 2012 Report Share Posted January 8, 2012 ...but then the cost of the helium outweighs the cost of the pick and mix I guess its all relative to the size of the balloon. key point, i think mythbusters did a similar thing but they were mailing packages of helium, and the cost of the helium basicly ruined any money saved. but yes the helium would reduce the weight of your sweets... Quote Link to comment Share on other sites More sharing options...
Muel Posted January 8, 2012 Report Share Posted January 8, 2012 I think this situation needs a Simps with some complicated maths to find the perfect cost of helium/saving made on sweets ratio. Quote Link to comment Share on other sites More sharing options...
JT! Posted January 8, 2012 Report Share Posted January 8, 2012 The reason you're getting confused is you're starting from the position of: 'More mass = more weight'. This is true in most circumstances, as weight is generally mass*gravity, gravity being a constant number. However in the situation you're talking about, you're adding more mass (helium + balloon materials) to the bag, even though that mass will be creating a opposite force. It's like asking how much you weigh when you're in water. Or free falling from a plane. In both these situations your mass stays the same, but the word 'weight' becomes ill defined. Tying a helium balloon to the bag will most certainly make it weigh less even though you're adding mass. And you will get your sweets cheaper. But I think the person selling you the pick and mix will have issue with it. It would also not make much of a difference. You're average helium balloon will barely lift a pound coin half the time. You might save 2p at best. ...but then the cost of the helium outweighs the cost of the pick and mix I guess its all relative to the size of the balloon. Helium will always cost more than the money saved on the pick and mix. However hydrogen is as twice as light as helium, so you'd get more for your money with that. Just don't go near any naked flames. It's all relative to the ratio between the balloon materials and the helium. You could probably fill a hot air balloon with helium and it wouldn't go anywhere because the materials on a hot air balloon would outweigh the helium. Quote Link to comment Share on other sites More sharing options...
Muel Posted January 8, 2012 Report Share Posted January 8, 2012 For a cheap option, turn the bag upside down and light a fire under it? Quote Link to comment Share on other sites More sharing options...
george_seamons Posted January 8, 2012 Author Report Share Posted January 8, 2012 Especially benificial with marshmallows! Quote Link to comment Share on other sites More sharing options...
manuel Posted January 8, 2012 Report Share Posted January 8, 2012 For a cheap option, turn the bag upside down and light a fire under it? or go to a supermarket before a film ... 1 Quote Link to comment Share on other sites More sharing options...
Muel Posted January 8, 2012 Report Share Posted January 8, 2012 Well personally I just don't eat sweets at all, but whatever works for you I guess. Quote Link to comment Share on other sites More sharing options...
Shaun H Posted January 8, 2012 Report Share Posted January 8, 2012 If you were weighing it in a vacuum then you would be correct (if we ignore all the ascociated impossibilities of a baloon in a vacuum that is). The problem you have is that you are weighing something that is actually in a fluid (air). All the sweets and the bag have a density that is far in excess of the air so their buoyancy (or lack there of) is negligible in this situation however the helium is less dense than the surrounding air and therefore floats in it and would actually reduce the weight of the bag. You could say technically the bag does "weigh" more in terms of mass. It would take slighly more energy to accelerate it horizontally for instance. But since the helium is lighter than the surrounding air it will try to float up and therefore the scale would show a slightly lower measured weight. An easier example might be an underwater scale with a small piece of concrete and a large log. Now the log could be heavier than any man could lift, yet the underwater scale will never be able to measure it's weight as it will float up in the water whereas the dense concrete can be placed on the scales and weighed (although the weight shown would be less the displaced water weight). I hope that's understandable, I'm very tired and have had several pints tonight! Quote Link to comment Share on other sites More sharing options...
isitafox Posted January 8, 2012 Report Share Posted January 8, 2012 Well from what I've read (well, skimmed over) the common sense answer still hasn't been said. If the pick n mix bag has a helium balloon in it then you wouldn't fit as much sweets in so it's a shite idea, though it would be cheaper because of this.Well from what I've read (well, skimmed over) the common sense answer still hasn't been said. If the pick n mix bag has a helium balloon in it then you wouldn't fit as much sweets in so it's a shite idea, though it would be cheaper because of this. Quote Link to comment Share on other sites More sharing options...
Tomm Posted January 8, 2012 Report Share Posted January 8, 2012 What you'd need for some real money saving is some sort of high pressure vessel filled with helium at high pressure. More helium = more floaty. P.S. If you've been on this forum less than 5 years, you probably won't get this reference 4 Quote Link to comment Share on other sites More sharing options...
isitafox Posted January 8, 2012 Report Share Posted January 8, 2012 What you'd need for some real money saving is some sort of high pressure vessel filled with helium at high pressure. More helium = more floaty. P.S. If you've been on this forum less than 5 years, you probably won't get this reference Quote Link to comment Share on other sites More sharing options...
JD™ Posted January 9, 2012 Report Share Posted January 9, 2012 Exactly his point in the 'p.s' bit Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted January 9, 2012 Report Share Posted January 9, 2012 So does the plane take off? Sorry, someone had to! Quote Link to comment Share on other sites More sharing options...
JD™ Posted January 9, 2012 Report Share Posted January 9, 2012 Yes. Quote Link to comment Share on other sites More sharing options...
Fish-Finger-er Posted January 9, 2012 Report Share Posted January 9, 2012 What you'd need for some real money saving is some sort of high pressure vessel filled with helium at high pressure. More helium = more floaty. P.S. If you've been on this forum less than 5 years, you probably won't get this reference interesting concept, I wonder if that could be made to work on bike frames, maybe fill the tubes with helium at like 10bar, and youve got a bike that weights nothing, possibly?!?! Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted January 9, 2012 Report Share Posted January 9, 2012 S'allllll about them titanium holes... 2 Quote Link to comment Share on other sites More sharing options...
ogre Posted January 9, 2012 Report Share Posted January 9, 2012 was hoping i'd be first in with titanium holes surely pressurised helium in a container 1cm^2 would offer more lift than the same 1cm^2 container of lower pressure? Quote Link to comment Share on other sites More sharing options...
JT! Posted January 9, 2012 Report Share Posted January 9, 2012 What you'd need for some real money saving is some sort of high pressure vessel filled with helium at high pressure. More helium = more floaty. P.S. If you've been on this forum less than 5 years, you probably won't get this reference Might be the first time I've ever felt OG on this forum! But what I never got about pressurized helium is that it's lighter than air because it's less dense? So helium pressurized would make it more dense and therefor heavier? S'allllll about them titanium holes... Quote Link to comment Share on other sites More sharing options...
isitafox Posted January 9, 2012 Report Share Posted January 9, 2012 interesting concept, I wonder if that could be made to work on bike frames, maybe fill the tubes with helium at like 10bar, and youve got a bike that weights nothing, possibly?!?! http://www.bikeradar.com/news/article/500g-barrier-shattered-by-groundbreaking-new-frame-25600/ Tryall should integrate this on their carbon fork Quote Link to comment Share on other sites More sharing options...
JT! Posted January 9, 2012 Report Share Posted January 9, 2012 interesting concept, I wonder if that could be made to work on bike frames, maybe fill the tubes with helium at like 10bar, and youve got a bike that weights nothing, possibly?!?! It would weigh nothing, but it's mass would increase. Making the bike harder to move in every direction that isn't against gravity. I wonder what the mass of a 1000 liters of helium would me compared to the mass of a 10kg bike. Quote Link to comment Share on other sites More sharing options...
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