Separation of Steel Balls in a Mixture: Understanding Particle Size and Density

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Discussion Overview

The discussion revolves around the phenomenon of separation in a mixture of steel balls of different sizes but the same density when subjected to shaking. Participants explore the underlying reasons for this behavior, drawing parallels to other examples such as the Brazil Nut Effect.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why separation occurs in a mixture of steel balls of the same density when shaken.
  • Another participant references the Brazil Nut Effect, suggesting that larger particles tend to rise to the top in mixtures, prompting further exploration of this effect.
  • A comparison is made to farmers needing to clear large stones from fields, indicating a similar phenomenon of larger objects moving to the surface.
  • Concerns are raised about the lack of explanation for why smaller particles settle at the bottom despite having the same density as larger particles.
  • One participant proposes that smaller particles can fall into the spaces between larger particles during shaking, allowing them to move downward, while larger particles cannot easily move through the smaller ones.

Areas of Agreement / Disagreement

Participants express differing views on the explanation of the separation phenomenon, with some agreeing on the mechanics of particle movement while others seek further clarification on the underlying reasons.

Contextual Notes

The discussion highlights assumptions about particle behavior and the conditions under which these observations are made, but does not resolve the complexities of the phenomenon.

Who May Find This Useful

This discussion may be of interest to those studying physics, materials science, or anyone curious about particle dynamics and segregation phenomena.

crx
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why in a mixture of different size same density steel balls we have a separation when shaken?
 
Last edited:
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When you open a can of mixed nuts, why are the Brazil nuts on top? The segregation of large and small nuts is called the Brazil Nut Effect. Do a google search on the Brazil Nut Effect.

I searched on "Brazil Nut Effect" in quotes and got 179,000 hits.

Bob S
 
For the same reason, farmers keep having to clear their fields of large stones and boulders, which constantly find their way to the surface.
 
sophiecentaur said:
For the same reason, farmers keep having to clear their fields of large stones and boulders, which constantly find their way to the surface.

But why does it happening? Even when all the components have the same density it seems that the larger particles falls slower than the small particles...
 
Bob S said:
When you open a can of mixed nuts, why are the Brazil nuts on top? The segregation of large and small nuts is called the Brazil Nut Effect. Do a google search on the Brazil Nut Effect.

I searched on "Brazil Nut Effect" in quotes and got 179,000 hits.

Bob S

and nobody can explain the reason why small particles get at the bottom!
 
crx said:
and nobody can explain the reason why small particles get at the bottom!
Yes they can. If you have a mixture of large and small particles, the small one can fall in between the big ones every time the mixture is shaken, and take small steps toward the bottom. On the other hand, the big one cannot fall through spaces between little ones. It is very hard for the big ones to push small ones up.
Bob S
 
The above post says it all.
 

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