Hot air balloons work on the scientific principle that warmer air rises in cooler air. Actually, hot air is lighter than cool air, because it has less mass per unit of volume. A cubic foot of air weighs roughly 28 grams. If you heat that air by 100°F, it weighs about 7 grams less. Therefore, each cubic foot of air contained in a hot air balloon can lift about 7 grams. Since there are 28 grams in one ounce, and 16 ounces to a pound, 7 grams isn't much weight. This is why hot air balloons are so huge. To lift 1000 pounds, you need about 65,000 cubic feet of hot air!
How many cubic feet of air do you need to lift 800 pounds?
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