Does a Vacuum Float?



I have a container that itself floats on water. The container has two compartments. The first contains pure Hydrogen at sea level pressure. The other is a vacuum… no air at all. Why would one side float while the other sinks? I’ve got it in my head that the vacuum side is neutral when it comes to weight, or that Hydrogen is somehow lighter.

Would it be different with 25% normal air in each side?

In: Chemistry

> Why would one side float while the other sinks?

It doesn’t. Things float because of the water they displace provides buoyancy. Hydrogen lightens the container and helps, but a vacuum has no effect.

Floating is all to do with weight compared with volume of water. If an object can displace a volume of water that weighs more than the object does, before the water level engulfs it, then it will float. For simple solid objects this is as simple as them being less dense than the water.

In your example if the container floats when filled with air (which is what I assume you mean when you say

> the container itself floats on water

), then it should float when filled with hydrogen, or when evacuated; since in both of these cases it would weigh less than when filled with air.

The side with the vacuum would be lighter assuming they are both identical

Vacuum is lighter than anything, including hydrogen, it has nothing inside, the problem is that vacuum containers need to be pretty sturdy to prevent them from getting crushed, so they would need to be very heavy completely defeating the point

Using a light gas like hydrogen or helium at the same pressure as outside is the solution, because now it doesn’t want to get crushed anymore, so you can use really lightweight balloons, so light that they can float because the over wall weight of the gas and ballon is less dense than the air around.

Keep in mind that floating isn’t really an upwards force so much as it’s a lack of a downwards force. Everything else in the world has a greater downwards force (weight) so the container gets shoved out of the way.

Displacement determines if something floats or not, if the item is more dense than the thing it floats in.

Ice, which is water, floats in water. How can this be? Density. Water expands as it turns into Ice, which lowers the density of the ice, which makes it ‘float’.

Hot Air Balloons float, but they are just full of hot air and they are not even sealed at all. How can this be? Density, once again. Hot air expands, which means it also loses overall density, which they trap in a balloon, which wants to ‘float’ on the other cooler air around it.

SCUBA tanks are absolutely full of many cubic feet of ‘air’, but they clearly sink when put in water. Why? Again, density… The air has been compressed, which increased the density, and it reduces the volume it takes up. And the new aluminum tanks show this even more clear, because they will sink when full of air–but float when empty.