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

  • Context: High School 
  • Thread starter Thread starter Bow Hunter Brandon
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Discussion Overview

The discussion revolves around understanding water displacement and buoyancy, specifically in the context of how much water needs to be displaced for a person weighing 160 lbs to float. Participants explore concepts related to density, buoyancy, and the implications of body composition on floating, with references to Archimedes' principle.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant calculates that to float, a person weighing 160 lbs would need to displace approximately 2.58 cubic feet of water, based on the weight of water.
  • Another participant questions the initial premise, suggesting that people typically float on the surface rather than displacing water in a submerged manner.
  • Some participants introduce the idea that body density affects buoyancy, noting that individuals with higher fat percentages may float more easily than those with higher muscle mass.
  • There is a discussion about the relationship between weight, volume, and density, with one participant explaining that a person must be less dense than water to float.
  • A later reply emphasizes that fat percentage and lung volume are significant factors influencing buoyancy.
  • One participant clarifies that they meant to refer to floating in a boat rather than floating in water directly, indicating a need for further simplification in their explanation.
  • Another participant suggests that Archimedes' principle can be applied to understand the situation better, referencing the balance of forces when floating.

Areas of Agreement / Disagreement

Participants express a mix of agreement and confusion regarding the concepts of buoyancy and displacement. While some agree on the calculations related to displacement, others introduce variables that complicate the discussion, indicating that multiple competing views remain.

Contextual Notes

There are unresolved assumptions regarding the definitions of buoyancy and displacement, as well as the implications of body composition on floating. The discussion also reflects varying levels of understanding among participants.

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?
 
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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...
 
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
 
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.
 
Last edited by a moderator:
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
 
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…
 


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
 
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?
 
It helps me clear out a few cobwebs from out of my head. Thanks!
 
  • #10
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.
 
  • #11
The same discussion applies.

- Warren
 
  • #12
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
 

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