How does Archimedes' Principle work?

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Discussion Overview

The discussion centers around Archimedes' Principle, specifically exploring the mechanisms behind buoyancy and fluid displacement. Participants examine how the weight of displaced fluid relates to the buoyant force experienced by objects submerged in a fluid, with a focus on conceptual understanding rather than mathematical derivation.

Discussion Character

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

Main Points Raised

  • Some participants describe Archimedes' Principle as stating that the weight of the fluid displaced is equal to the buoyant force, questioning how this occurs.
  • One participant suggests that the fluid's tendency to fall creates an upward force that pushes objects out of the way, contributing to buoyancy.
  • Another participant uses a thought experiment involving a plastic bag of water and a plastic bag of steel to illustrate that the upward force equals the weight of the displaced water, regardless of the object's material.
  • Some participants express a desire to understand the relationship between fluid displacement and buoyancy more deeply, questioning the underlying mechanisms.
  • One participant introduces the concept of pressure differences due to liquid depth, explaining that the upward force on an object is greater than the downward force, leading to buoyancy.
  • Another participant acknowledges the explanation regarding pressure and depth, indicating that it clarified their understanding of buoyancy.
  • There is a discussion about a diagram where some participants argue that buoyancy would be zero if the displaced liquid is removed, while others counter that the water above the object still contributes to buoyancy.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and agreement regarding the mechanisms of buoyancy and fluid displacement. Some concepts are clarified, but there remains disagreement about specific interpretations and implications of the diagrams discussed.

Contextual Notes

Some participants' arguments rely on specific assumptions about fluid behavior and pressure that are not universally accepted. The discussion does not resolve the complexities of these assumptions or the implications of the diagrams presented.

AudioFlux
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the Archimedes' Principle states that the weight of the fluid displaced is equal to the buoyant force. why/how does that happen?
 
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The fluid is trying to fall below you, and has to push you up and out of the way to do so.
 
Imagine a container of water and picture a volume of the water at some depth in the container. It might help to imagine this volume of water in a plastic bag (ignore the weight of the bag...it is only to help your imagination).
This volume of water will not be sinking or rising so the effect of the rest of the water in the container is to provide a force upwards equal to the weight of the water in the plastic bag.
Now replace the plastic bag of water with an identical volume plastic bag of steel. The water in the container continues to provide an upward force equal to the weight of water that was originally in place. Upward force on steel equals upwards force on weight of water that steel has replaced.
No equations, no complicated maths... hope it helps you cope with any equations and maths that you may meet.
 
jetwaterluffy said:
The fluid is trying to fall below you, and has to push you up and out of the way to do so.

but if that happens, then the diagram on the right has buoyancy=0, because the liquid displaced has been removed.
 

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technician said:
Imagine a container of water and picture a volume of the water at some depth in the container. It might help to imagine this volume of water in a plastic bag (ignore the weight of the bag...it is only to help your imagination).
This volume of water will not be sinking or rising so the effect of the rest of the water in the container is to provide a force upwards equal to the weight of the water in the plastic bag.
Now replace the plastic bag of water with an identical volume plastic bag of steel. The water in the container continues to provide an upward force equal to the weight of water that was originally in place. Upward force on steel equals upwards force on weight of water that steel has replaced.
No equations, no complicated maths... hope it helps you cope with any equations and maths that you may meet.

that's cool, but i have already understood how buoyancy is the same for equal displacement of the volume of a fluid. i wanted to know what the displacement of the volume of a fluid has to do with buoyancy and how the mechanism works.
 
The only extra that I can add involves talking about pressure due to a depth of liquid.
If the top of your container is h1 below the surface then the pressure on the top of the container is P = h1ρg and the force on the top of the container is P x A = h1ρgA
Similarly the force on the bottom is h2ρg if the bottom is at a depth of h2.
The upwards force is therefore greater than the downwards for by (h2-h1)ρgA
but this is the weight of the liquid that would occupy the same volume as the oject.
So the upthrust = weight of displaced liquid...(it does not matter whether the displaced liquid came out of the container or not)
I hope this adds to the explanation for you
 
technician said:
The only extra that I can add involves talking about pressure due to a depth of liquid.
If the top of your container is h1 below the surface then the pressure on the top of the container is P = h1ρg and the force on the top of the container is P x A = h1ρgA
Similarly the force on the bottom is h2ρg if the bottom is at a depth of h2.
The upwards force is therefore greater than the downwards for by (h2-h1)ρgA
but this is the weight of the liquid that would occupy the same volume as the oject.
So the upthrust = weight of displaced liquid...(it does not matter whether the displaced liquid came out of the container or not)
I hope this adds to the explanation for you

thanks you, that answered my question :)
 
AudioFlux said:
but if that happens, then the diagram on the right has buoyancy=0, because the liquid displaced has been removed.

In that diagram the ball still has water above it. This water is attracted towards the ground.
 
jetwaterluffy said:
In that diagram the ball still has water above it. This water is attracted towards the ground.

oh. right
 

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