Hia, Im not a student, im a gas engineer in the UK. Had a thought and tried out some theory but didn't get very far. Basically; if a helium ballon rises in air as it is lighter than the air it displaces, what if I could get a tube (say internal dimensions of 15mm in diameter and 1000mm long making a volume of 0.177m^3 (ish)) and create a vacuum within it. obvously serous levels of vacuum would be difficult to achieve so im not looking to go too far down with it. (oh and in case your wondering why I picked a tube, I figure it's easier to work with than a sphere, less likly to collapse. Can't remember why, I think thats how it works. (and if it works it'll be more fun to play with!!!) Can anyone help me pick a suitable material to make the tube from? Any ideas how thick the wall would need to be etc... Oh and a thought ive had just this seond. If I filled the tube with helium then vacuumed that out, then the bits I can't be bothered to wait for would be ligher than air anyway. Any help would be greatly appreciated.