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# Noble Gases

## Characteristics of Group 18 of the periodic table.

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Lighter than Air

### Lighter than Air

Credit: D. Miller
Source: http://www.flickr.com/photos/92653143@N00/2748277241

This blimp is a common sight at professional football games and other outdoor events. A blimp is a type of lighter-than-air flying machine. It floats on air like a boat floats on water. Most blimps, including this one, are used for advertising.

#### The Back Story

• Blimps aren’t the only type of lighter-than-air flying machines. Another type is the airship, sometimes called a zeppelin. Blimps are like big balloons with no internal structure. Airships, on the other hand, have a lightweight internal frame that makes them rigid even when they aren’t filled with gas.

Without helium, this zeppelin would not be able to rise up into the air [Figure2]

• Both blimps and airships rise up into the air because they are filled with helium, a noble gas that is less dense than air. The helium gives the aircraft buoyancy in the air, just as a floating ship has buoyancy in the water.
• Both blimps and airships also have engines, but they are used just to move the aircraft forward. They are not used to lift the aircraft off the ground or keep it up in the air.
• You can see what it’s like to ride in an airship by watching this video: http://www.exploratorium.edu/tv/index.php?project=104&program=1361&type=clip

#### Can You Apply It?

1. Why do rigid airships have to be above a certain size in order to rise off the ground?
2. What is buoyancy? How does it apply to blimps and airships?
3. What is Archimedes’ Law (Principle)? How does it apply to blimps and airships?
4. Lighter-than-air craft now use helium for lift. In the past, they used hydrogen. Contrast the lifting force and availability of hydrogen and helium. Why is helium used instead of hydrogen for blimps and airships?

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