Re: Could a vacuum chamber be used to make something float in water?

Hello Nicholas,

Thank you for your question. You asked whether a vacuum would make something float. To answer your question, we will investigate what makes things float.

If an object is put into a liquid, it will displace some of this liquid. Displacing this liquid takes energy, as the only way for the liquid to go is up. This is known as Archimedes' Principle: if an object is put in a liquid, the liquid exerts a buoyant force equal to the weight of the displaced liquid. You can test this yourself by trying to force a balloon underwater: this is pretty hard, because you need to displace an amount of liquid which is equal in volume to the volume of the balloon, and this can be quite a bit

For the buoyant force, it does not matter what material is displacing the liquid. In fact, a vacuum could displace the liquid, of course providing it is in a closed container, for instance a metal drum. So yes, a vacuum would help in making an object float. It would however exert just as much buoyant force as air, or another gas. The only difference would be the weight of the air. Air has a mass of about 1.2 kg per cubic meter, while a vacuum has no mass nothing, so this difference would be really small compared to the mass of one cubic meter of displaced water, which has a mass of 1000 kg. To make matters worse, in practice, a vacuum vessel has to be quite strong to maintain a vacuum inside without imploding. Hence, in reality, a vessel relying on a vacuum to stay buoyant would probably work a lot less good than one that relies on air.

As a compromise, you could consider using a lighter gas, such as hydrogen, which is the lightest gas. Hydrogen is about 7 times lighter than air. Still. this only increases the net buoyancy per cubic meter by 1 kg, in other words, an increase of 0.1%. This doesn't really help a lot, especially considering how hard it would be to make such a thing in practice

In a nutshell, we can say a vacuum would help to make things float. However, air would work (almost) as good, so there is little point in using a vacuum.

I hope this answers your question.

Regards,

Bart