Scientists who perform atmospheric research use helium-filled weather balloons to carry various measuring instruments into the atmosphere. One group who does this is NASA. You are probably familiar with the Goodyear blimp , which uses helium to stay afloat. The Goodyear blimp website contains technical information about the blimps, including their volumes and maximum gross weights. If you use the ideal gas law, the molecular weights shown above and the appropriate unit conversions, you should calculate gross weights close to those stated on the web site.
There is, of course, one gas that is even less dense than helium, and that is hydrogen, whose molecular weight is 2. One liter of hydrogen would thus lift 1. Hydrogen was indeed used in the early days of dirigibles, the most in famous of which was the Hindenburg. While it is still not known for certain whether the hydrogen itself was responsible for the disaster of the Hindenburg, the eight percent increase in weight capacity over that of helium is not worth the risk of using such an inflammable gas.
Therefore, if you were to fill a 1-liter soda bottle full of helium, the bottle would weigh about 1 gram less than the same bottle filled with air. That doesn't sound like much -- the bottle itself weighs more than a gram, so it won't float. However, in large volumes, the 1-gram-per-liter difference between air and helium can really add up. This explains why blimps and balloons are generally quite large -- they have to displace a lot of air to float.
The following diagram shows the different lifting capacities of different volumes of helium:. A foot-diameter balloon can lift 33, pounds! Here is how you can figure out the lifting capacity of the helium in a spherical helium balloon:. So, for example, a foot balloon has a radius of 10 feet. Although not used much anymore, hydrogen balloons were once quite popular.
Hydrogen weighs just 0. However, it is highly flammable, so the slightest spark can cause a huge explosion. So why are helium and hydrogen so much lighter than air? It's because the hydrogen and helium atoms are lighter than a nitrogen atom. They have fewer electrons, protons and neutrons than nitrogen atoms do, and that makes them lighter the approximate atomic weight of hydrogen is 1, helium is 4 and nitrogen is And since it was sitting on the bench I switched in on and lifted it up and despite the fact that I expected it to happen, I was amazed to see the pressure fall by around 10 Pascals as I lifted it up above my head, and then to increase again as I put it back on the bench.
Now this fall is only 0. And I thought this was an example where the ability to simply measure something directly really gave an extra insight into the way the world worked. This entry was posted on September 10, at pm and is filed under Simple Science. You can follow any responses to this entry through the RSS 2. You can leave a response , or trackback from your own site.
I was surprised to see the sensitivity to a couple of meters as well. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email.
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