Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Fiona on 19/04/2011 11:30:02

Title: How much O2 is needed to lift a 1kg mass in water?
Post by: Fiona on 19/04/2011 11:30:02

Fiona  asked the Naked Scientists:
   
Hi Chris, really love your site (http://www.thenakedscientists.com/HTML/podcasts/).  Need some help with a coefficient for:
 
In water (ie a lake), how much O2 is needed to lift 1 Kg of Mass?
 
Thanks for your assistance.
Best Regards
Fiona

What do you think?

Title: How much O2 is needed to lift a 1kg mass in water?
Post by: RD on 19/04/2011 12:01:37

If by "O2" you mean air, it's mostly N₂ ...

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2F7%2F7a%2FAtmosphere_gas_proportions.svg&hash=26448152ef904527fcc7c711805a6731)

http://en.wikipedia.org/wiki/Air#Composition

Further reading ...

http://en.wikipedia.org/wiki/Air#Density_and_mass

http://en.wikipedia.org/wiki/Boyancy

Title: How much O2 is needed to lift a 1kg mass in water?
Post by: Phractality on 19/04/2011 16:38:13

To float, the 1 kg mass plus the mass of O₂must displace an equal or greater mass of water. So the mass of O₂depends on the density and depth of the water and the density of the 1 kg mass. If you have a balloon full of O₂which is just big enough to make the 1 kg mass float at the surface, and you then pull it below the surface, the balloon will shrink as the pressure increases. Below a certain depth, it will sink.

Title: How much O2 is needed to lift a 1kg mass in water?
Post by: JP on 19/04/2011 16:43:56

You need no O₂ to make 1 kg of ice float.  :)

(Which is due to it's density being lower than water, as others have pointed out.)

Title: How much O2 is needed to lift a 1kg mass in water?
Post by: Geezer on 19/04/2011 20:16:36

I don't think we have enough information to answer the question. As Phrac points out, the lift is a function of the depth, so, if you want to lift something from the bottom of the lake, you'll need to know how deep the lake is.