How does a big heavy balloon with a basket full of people manage to float in the air?
How does a big heavy balloon with a basket full of people manage to float in the air?
Hot-air balloons float because the air trapped inside the balloon is heated up by a burner, making it less dense than the air outside. Here's another way to think of it. You've probably heard people say that heat rises, by which they really mean that hot air rises. When you see clouds of dirty gray gas drifting upward from smokestacks, that's because the air coming out of them is hotter than the ambient (surrounding) air. If you could wrap a bag around the hot air entering the bottom of a smokestack, and seal it up, the whole bag would shoot upward and come out of the top before zooming off and up into the air. In effect, you'd have made a tiny little hot air balloon!
Tiny balloons aren't actually much use, however. If you want to carry a heavy weight on the sea, you need a big ship: one that can displace more water can carry more load. In exactly the same way, you need a big hot-air balloon to lift a big weight—because you need to create more lift with a larger volume of hot gas. Just to lift an adult man's weight, you'd need a balloon about 4m (13ft) in radius with the air inside heated to a temperature of about 120°C (250°F). That explains why hot-air balloons are generally so large.
Hot-air balloons float because the air trapped inside the balloon is heated up by a burner, making it less dense than the air outside. Here's another way to think of it. You've probably heard people say that heat rises, by which they really mean that hot air rises. When you see clouds of dirty gray gas drifting upward from smokestacks, that's because the air coming out of them is hotter than the ambient (surrounding) air. If you could wrap a bag around the hot air entering the bottom of a smokestack, and seal it up, the whole bag would shoot upward and come out of the top before zooming off and up into the air. In effect, you'd have made a tiny little hot air balloon!
Tiny balloons aren't actually much use, however. If you want to carry a heavy weight on the sea, you need a big ship: one that can displace more water can carry more load. In exactly the same way, you need a big hot-air balloon to lift a big weight—because you need to create more lift with a larger volume of hot gas. Just to lift an adult man's weight, you'd need a balloon about 4m (13ft) in radius with the air inside heated to a temperature of about 120°C (250°F). That explains why hot-air balloons are generally so large.
