From Wired Science: How the house in the recently released film “Up” could actually fly. I love scientists!
First they called a house moving company to see how much a house like that would weigh. Kendal Siegrist at Wolfe House Movers estimated the house would be around 100,000 pounds.
Then we did some calculations. Air weighs about 0.078 pounds per cubic foot; helium weighs just 0.011 pounds per cubic foot. A helium balloon experiences a buoyant upward force that is equal to the air it displaces minus its own weight, or 0.067 pounds per cubic foot of helium balloon.
One more simple calculation — 100,000 pounds divided by 0.067 pounds per cubic foot — and you’ve got that it would take 1,492,537 cubic feet of helium to lift the house. Of course, you’d need some more balloons to keep getting it higher, but that’s our minimum.
Now, let’s assume you’ve got a bunch of spherical balloons three feet in diameter. They’ve got a volume in 14.1 cubic feet, so you’d need 105,854 of them filled with helium to lift the house. Eyeballing the cluster of balloons above the house in Up, let’s say on average, it’s 40 balloons across and deep and 70 balloons tall. Do the math and there could be 112,000 balloons in there.
Read the full analysis at Wired Science.