How Vacuums Work

Announcer

Welcome to Brain Stuff from howstuffworks.com, where smart happens.

Marshall Brain

Hi. I’m Marshall Brain with today’s question. Would a balloon filled with vacuum instead of helium float? At sea level, air weighs about 1.25 grams per liter. A liter of helium, on the other hand, weighs about .18 grams. If you weigh a one-liter bottle filled with air and then weigh the same bottle filled with helium, it will weigh about one gram less.

If the bottle itself weighed less than a gram, you couldn’t weigh it at all because it would float. You would have to turn the scale upside down and put it above the floating bottle to check its negative weight. Generally, a balloon has to be several liters in size before that one gram per liter weight difference of helium versus air is enough to overcome the weight of the balloon itself and float.

If you could somehow fill a one-liter bottle with a vacuum, it would float even better. A perfect vacuum weighs zero grams, so a liter of perfect vacuum weighs zero grams, and that’s .18 grams less than a liter of helium. The problem, of course, is that building a lightweight container that could hold a vacuum is not nearly as easy as building a container that can hold helium.

The phrase, “Nature abhors a vacuum,” sums it up nicely. If you could figure out a way to do it, however, you would be set. Your vacuum balloon would float even better than a helium balloon. Note that you don’t need to have a perfect vacuum for this to work. Any air that you take out of the container helps a vacuum balloon to float.

Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at howstuffworks.com.

Announcer

For more on this and thousands of other topics, go to howstuffworks.com.