A question of lifting bodies underwater

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Discussion Overview

The discussion revolves around the buoyancy of two rubber-coated Kevlar balls, one filled with air and the other with helium, when submerged underwater. Participants explore the implications of buoyancy and the compressibility of gases in this context.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions whether the helium-filled ball would be harder to keep underwater compared to the air-filled ball, seeking clarification on their buoyancy.
  • Another participant asserts that the buoyancy is the same for both balls, but notes that the helium-filled ball is lighter, resulting in a higher net force required to keep it submerged.
  • A third participant agrees with the previous point but emphasizes that the difference in lifting forces is minimal, suggesting that precise measurement would be necessary to detect it.

Areas of Agreement / Disagreement

Participants generally agree on the concept of buoyancy being the same for both balls, but there is a nuanced discussion regarding the implications of the weight difference and the practical detectability of this difference.

Contextual Notes

The discussion does not resolve the question of how compressibility affects buoyancy in practical terms, nor does it clarify the assumptions regarding the conditions of the experiment.

Dr Quest
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If I have two rubber coated kevlar balls, one is filled with air and the other has a gas like helium in it, if submerged underwater, would the ball with helium be harder to keep underwater than the air filled ball would be, or would they be equal in their buoyancy?
Also is helium easier to compress than air, I would imagine it would be but I don't have any schooling in this field.
Thanks for the site, and any answers to my questions.
 
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The way the definition of buoyancy works, the buoyancy is the same - what is different is the weight of the two gas-filled spheres. Since the one filled with helium is lighter, the net force required to keep it submerged is higher.
 
Russ_watters is right. But you cannot feel the difference. You must measure the two lifting forces with a very precise device. The difference in lift is about 0.1%.
 
Thanks for the info!
 

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