Last night in the pub, got talking with builder friends about expanding foam. None of us have a definatife answer to the point put forward which is : IF A 500G TIN (contents ) were squirted into a box or something, would the final 'product' weigh 500gm or more / less due to expansion. No one was that confident of thier answer that no beer was waged on the outcome. So if any budding scientists know a correct answer I would be grateful.
The foam is produced by the compressed gas stored within the fluid in the can "boiling" when it exits the nozzle, due to the sudden change in relative environmental pressure. This boiling causes the gas that hasn't inflated the bubbles to produce the foam, will escape to atmosphere giving the smell you get from the foam. With an amount of the can contents escaping, the foam will weigh less, but not by much. It's worth remembering that there will be more than the stated weight in the can to stop the manufacturer getting sued for under filling the can.
Martin, you should be doing my job selling foam!!
[quote=zoidberg;474718]Last night in the pub, got talking with builder friends about expanding foam. None of us have a definatife answer to the point put forward which is : IF A 500G TIN (contents ) were squirted into a box or something, would the final 'product' weigh 500gm or more / less due to expansion. No one was that confident of thier answer that no beer was waged on the outcome. So if any budding scientists know a correct answer I would be grateful.[/quote] Totally different type of foam to what I'm involved in, but I would agree with what Martin has already said. I usually talk about women and football when I'm on the razz, but I might bring the subject of foam up next time I'm with me mates and see how long the conversation lasts!lol
It's a bit like saying which weighs more - 500g of feathers or 1/2kg of lead. Don't confuse mass with density. Weight is relative to the acceleration due to the force of gravity. Expanding foam polyurethane foam is created by a reaction between isocyanates & water in the can, to create carbon dioxide bubbles, which are trapped by the long polymer chains. Law of conservation of matter states that matter cannot be created or destroyed - it just transfers from one state to another. However because the water will evaporate at - the dried solution will weigh ever so slightly less. Depends when you measure it.
It's a bit like the old question about the wagon carrying birds. If it goes on to a weighbridge and you bang on the side of the wagon to get all the birds flying will the wagon weigh any less? The answer is --------- - -- ----- ------- ================ No. Well I did have to give you time to think. :smile:
I think the box would be heavier, because of the trapped air.
In theory it would weigh very slightly less, the reaction that creates the foam does not draw anything from the atmosphere to add weight, some of the gas that is created by the reaction between the two constituant parts will escape to air, and so by default will weight less. I would imagine that you would need some very sensative scales to measure the difference. Id also imagine that you would either have to be extremely sad or extremely bored ( or extremely drunk !) to want to try the experiment. We normally talk about really daft things in the pub.... like attaching 10 kenetic energy ropes together, attaching one end to a stout tree and the other to a no so stout car......... Fortunately in the cold light of day we decided that was probably a daft idea.. plus we couldnt find any one prepared to drive the car away from the tree at speed.
Isn't that what I said? The CO2 is created by the reaction between the water & isocyanates - creating long polymer chains with the gas trapped in them. you can see that when you cut the dry stuff in half - full of bubbles.
Also does it not produce heat ? Its been a long while since I used this stuff, if it produces heat then thats an additional weight loss ( although again, so small its proabaly not measurable) And yes Dave .... thats excatly what you said :-)
It is an exothermic reaction. I guess any water left behind will eventually evaporate. But to all intents & purposes the weight will remain the same.