[Physics] Balloon, lighter than air and vacuum


As I understand, in a balloon/air balloon, a gas burner is used to heat air or using some lighter atom like helium. Since helium or hot air is lighter and less dense than the cool air around the balloon, the heated air or helium causes the whole balloon to rise. And as I understand, vacuum is a space where there are no atoms inside. So no atom inside means it's lighter than to have atom an inside? Isn't it? So why we can't make something fly by giving it a vacuum container?

Best Answer

I assume you are asking why we are not drawing air out of a balloon like container so as to create the lower density that helium or hot air gives us.

The answer is that it is hard to maintain a vacuum with a thin enough, so as to be almost weightless, rigid contaning surface. A balloon with gas inside equalizing the atmospheric pressure with the gas pressure is easy to make air tight and stable. A vacuum in a thin enough walled container would be liable to collapse, due to the atmospheric pressure, and would be hard to make air tight.