Re: Will a air tank with the air removed from it float in water?

Hi Scott

The question of whether something will float or not depends on density. The air 
inside something does not make it float. However, air is less dense than other 
materials, such as metals, so something that is mostly air will have a lower density 
and is more likely to float. You said that the tank already floats with atmospheric 
pressure inside. A tank that floats with air inside it will float even higher if the air is 
removed, as long as the volume of the container remains the same. 

Now, to the question of whether an air tank will float with 100 pounds per square 
inch of pressure. Atmospheric pressure is 14.7 pounds per square inch, so this is 
about 6.8 times atmospheric pressure. The density of air at sea level is about 
1.229 kg per cubic meter. If the pressure is increases 6.8 times, so will the density. 
The density would be 8.4 kg per cubic meter. Water density is 1,000 kg per cubic 
meter (about 62.3 pounds per cubic foot), so the air is much less dense. 

The unknown factor is how large the container is and what its empty mass is. If 
you know the size and mass, multiply the volume by the air density, which will give 
you the mass of the air. Add the mass of the air and the container together, then 
divide that by the volume. That will give you the average density of the container. 
If the average density is less than water, 1,000 kg per cubic meter, then the 
container will float.

I hope I've answer your question satisfactorily, Scott. Thanks,

Kevin