Understanding Water Displacement: How Much Water Do I Need to Float at 160 lbs?

[Bow Hunter Brandon]

First I want to say that some of these discussions are way over my head but others I find very interesting and I will continue to read through the threads just to exspand my understanding. I have tried a few searches and not found exacly what I am looking for so here it is.
I want to figure out what it will take to float myself in water.
My weight is 160 lbs and my understanding is that water is 62 lb per cubic foot for its weight. So to me that means 160/62= the amount of water I need to diplace to float myself or or 2.58 cubic feet of water needs to be diplaced. Is that correct?

 

[LogicalAtheist]

Uhm, float yourself? I think most people float on top of water normally, I sure do.

I go in the pool and lay down and I float on top, no problem at all. So I'm confused...

 

[chroot]

Originally posted by Bow Hunter Brandon
or 2.58 cubic feet of water needs to be diplaced. Is that correct?

Yep. You'll need to displace at least 2.58 ft³ of water to float.

- Warren

 

[BoulderHead]

I'm thinking that the density of your body needs to be factored into the equation. If you have a lot of 'blubber' you will be more buoyant than a lean person of equal weight with a higher level of muscularity.

[edit]
On the other hand, I'm thinking more along the lines of scuba diving, were a 'fattish' person will require more lead weights on his/her belt.

 

[chroot]

Originally posted by BoulderHead
I'm thinking that the density

What else do you think weight and volume would be used to determine? The statement a 162 lb man must displace more than 2.58 ft³ of water to float is equivalent to the statement the man must be less dense than water to float.

- Warren

 

[BoulderHead]

I think I confused myself.

I was thinking not of displacement, but how some people are more buoyant than others...
Does that make any sense? I’m confused…

 

[chroot]

Originally posted by BoulderHead
I was thinking not of displacement, but how some people are more buoyant than others...
Does that make any sense? I’m confused…

Fat percentage and lung volume are the two largest variables.

- Warren

 

[ahrkron]

Originally posted by Bow Hunter Brandon
My weight is 160 lbs and my understanding is that water is 62 lb per cubic foot for its weight. So to me that means 160/62= the amount of water I need to diplace to float myself or or 2.58 cubic feet of water needs to be diplaced. Is that correct? [/B]

I think this is correct (I have no idea about the numbers though).

The relation betwenn this and density is that the amount of water you displace is related to your volume.

Sometimes exagerating things help understanding. For instance, imagine you weight 160 lbs, and that you are extremely big, so that your legs already have a VOLUME of 2.58 cubic feet. This means that once you have submerged them, you already pushed away all the water you needed in order to float.

On the other hand, if you weight the same 160, but your whole body only occupies 2 cubic feet, then even if you sink completely you won't displace enough water to have a buoyant force equal to your weight.

Does that help?

 

[BoulderHead]

It helps me clear out a few cobwebs from out of my head. Thanks!

 

[Bow Hunter Brandon]

follow up

Im sorry I should of been more specific. I was trying to keep it simple and instead made it more difficult. By float myself in water I should of said float myself in a boat. In the example I should of said myself and the boat weight would be 160 lbs.

 

[chroot]

The same discussion applies.

- Warren

 

[schwarzchildradius]

eureka!
ok all kidding aside, you can use Archimedes principle here with no problem whotseuever.
ρ-naught/ρ-fluid = Volumme-fluid/Volume-naught
Also, since you're not accelerating when you're floating, the sum of the forces = ma = 0, so Bouancy force = mg = ρVolume