Can You Explain Why a Cork Won't Float in the Center of a Glass of Water?

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Discussion Overview

The discussion centers on the behavior of a cork in a glass of water, specifically why it does not float in the center. The scope includes conceptual understanding of buoyancy and surface tension, as well as practical experimentation.

Discussion Character

  • Exploratory, Conceptual clarification, Experimental/applied

Main Points Raised

  • Some participants suggest that the cork does not float in the center due to the surface tension of the water, which causes the water level to be higher at the edges of the glass compared to the center.
  • Others propose that it is possible to make the cork float in the center by carefully overfilling the glass with water, creating a situation where the cork can remain suspended in the middle.
  • A participant shares personal experience confirming that the method of overfilling works effectively.
  • There is a suggestion for creating a forum or reference links for interesting experiments, indicating a desire for collaborative sharing of knowledge and practical applications.

Areas of Agreement / Disagreement

Participants present differing views on the cork's behavior, with some agreeing on the influence of surface tension while others provide a method to achieve a different outcome. The discussion remains unresolved regarding the general principles at play.

Contextual Notes

The discussion does not address potential limitations or assumptions regarding the conditions under which the cork's behavior is observed, such as the specific shape of the glass or the amount of water used.

kath102245
Why is it that when you put a cork in a glass of water, it won't float in the center?
~Kathleen
 
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Because the water's surface is not flat. The water has surface tension, which tends to pull the water up along the edge of the glass. In other words, the water around the edge is higher than the water in the center. The cork seeks (via the buoyancy force) the highest position, which is at the edge.

- Warren
 
You can make the cork float on the center, though, if you're clever.

Fill a glass (with cork in it) to the brim with water. Slowly add water so the water goes slightly over the brim but does not spill. You'll find the cork now floats in the middle of the glass!
 
I just tried this with a cork - It works well.


Perhaps we should have a forum (or reference links?) of interesting experiments, along with an explanation of how they work. Between us all we must know hundreds of great, but simple, experiments. I suppose that this would be hard to arrange though...
 

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