You probably own dozens of books -- all of which started out as ideas. Go behind the scenes to see how an idea ends up on your bookshelf!

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­If you actually need to get somewhere, a hot air balloon is a fairly impractical vehicle.You can't really steer it, ­and it only travels as fast as the wind blows. But if you simply want to enjoy the experience of flying, there's nothing quite like it. Many people describe flying in a hot air ballo­on as one of the most serene, enjoyable activities they've ever experienced.

­Hot air balloons are also an ingenious application of basic scientific principles. In this article, we'll see what makes these balloons rise up in the air, and we'll also find out how the balloon's design lets the pilot control altitude and vertical speed. You'll be amazed by the beautiful simplicity of these early flying machin­es.

Hot air balloons are based on a very basic scientific principle: warmer air rises in cooler air. Essentially, 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 (about an ounce). If you heat that air by 100 degrees F, it weighs about 7 grams less. Therefore, each cubic foot of air contained in a hot air balloon can lift about 7 grams. That's not much, and this is why hot air balloons are so huge -- to lift 1,000 pounds, you need about 65,000 cubic feet of hot air.

If you’re interested in getting a birds-eye-view of the world, then you should check out the paragliding article, video and images at Discovery’s Fearless Plan­et.

In the next section, we'll look at the different components of hot air balloons to find out how they heat the air.