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What do you get when you put a duck, a sheep, and a rooster in a balloon heated by a fire pit of burning straw and manure? You get a place in the history books as being the first to demonstrate that flying is possible. This feat, credited to the Montgolfier brothers of France in 1783, began a fascination with ballooning that still exists today.
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!
To regulate the temperature of the air inside the balloon, you can do several things. If you want to go up, you can reheat the air inside the balloon by turning on a burner located under the open balloon. This burner works much like a gas grill or stove. You can increase the speed the balloon goes up by heating the air more rapidly. If you want to go down, you can decrease the inner temperature by opening up a parachute valve at the top of the balloon and letting out some of the hot air.
The bottom line: Increase the heat to make the balloon rise, and open the vent to make it sink. This covers vertical motion; but if you can't steer a balloon, how can you make it move horizontally? Actually, because wind blows in different directions at different altitudes, you can steer the balloon by going up or down to the right level and then riding the wind. And since wind speed usually increases as you get higher in the atmosphere, you can control your horizontal speed by changing the balloon's altitude.
So if you don't have anywhere in particular to go, but are looking for the thrill of flying, you may want to hitch a ride on a balloon.
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