Archimedes Principle: Weight of Immersed Object

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Discussion Overview

The discussion revolves around Archimedes' principle, specifically addressing the weight of an object that is partially immersed in water and the relationship between the weight of the displaced water and the weight of the object. The scope includes conceptual clarifications and technical explanations related to buoyancy and equilibrium conditions.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants clarify that Archimedes' principle states the buoyant force is equal to the weight of the displaced liquid, which leads to questions about whether this applies to the entire object or just the immersed part.
  • Others argue that for a freely floating object, the buoyant force must equal the weight of the entire object, while noting that partially immersed objects may involve additional forces.
  • One participant points out that equilibrium conditions affect the relationship between the weight of the displaced water and the weight of the object, providing examples with corks and concrete blocks.
  • Another participant inquires whether the weight of the displaced water can equal the weight of the part of the object below the water level, suggesting conditions where this might occur, such as when the object's density matches that of water.

Areas of Agreement / Disagreement

Participants express varying views on the relationship between the weight of displaced water and the weight of the immersed object, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants mention the importance of equilibrium and external forces, which may not have been fully defined or explored in the discussion.

Deebu R
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I was just a bit confused about Archimedes principle. Say an object is partially immersed in water. The weight of water water displaced will be equal to weight of the entire object or just the part immersed in water?
 
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Archimedes' principle states that the buoyant force on an object is equal in magnitude to the weight of the displaced liquid.

A corollary is that for a freely floating object on the surface, the buoyant force must exactly cancel the weight of the object. Since Archimedes' principle states that the buoyant force is equal in magnitude to the weight of the displaced liquid, the weight of the displaced liquid must be equal to the weight of the entire object or the object will not be floating.

Note that freely floating in not the same as partially immersed. For a partially immersed object, there may be other forces at work as well in addition to gravity and the buoyant force. In that situation, those forces must also be taken into account.
 
It depends: on whether there is equilibrium ! If you have to push down to keep a cork partially under water, the weight of the water is more than the weight of the cork. And if you have to pull up to keep a block of concrete halfway in the water, the weight of the water is less than the weight of the concrete.

But if a boat floats peacefully on the surface, then yes: the volume of water displaced weighs as much as the wole boat
 
Ah.ok. I understand. Thank you orodruin and BvU.
 
One more thing. Is there a case were the weight of water displaced equal the weight of the part of the body which is below water level?
 
Deebu R said:
One more thing. Is there a case were the weight of water displaced equal the weight of the part of the body which is below water level?
Yes, when there is nothing above the surface and the object has the same mean density as water.

Or when the remaining force to hold the object in place is provided by another external force.
 
I understand. Thank you
 

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