Properties of High Viscosity Liquids

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Main Question or Discussion Point

An object rests on a high viscosity liquid like jelly what properties of the liquid keep it from breaking the surface of the jelly and sinking. (object deforms surface but doesnt break it)
is it surface tension? Viscosity? How would the load carrying capacity of the jelly be tested?
 

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  • #2
alxm
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Surface tension, viscosity and density are all at work. Density because even if it hasn't broken the surface, it's still displacing some liquid. But mostly the former two are at work.

Surface tension and viscosity are closely-related properties though, as both are just measures of inter-molecular cohesion, albeit in two different circumstances.

Testing it would seem fairly straightforward?
 
  • #3
Andy Resnick
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Be careful- jelly is not simply a viscous fluid. Gels are materials displaying both fluid and solid properties- there may be a critical shear stress below which the material does not flow, and above which, the material flows (Bingham fluids, similar to toothpaste). There's also viscoplastic fluids (and many other types of materials) which can have very complex behavior.

So, if the pressure applied by the object is insufficient, the jelly can act as an elastic solid and deform. If the applied pressure is sufficiently high, the object may move through the material as a viscous fluid. Other, more complex, forms of motion may be observed as well.

Now, of course, if the jelly is hydrated and is allowed to form a thin dehydrated skin, the dynamics are much different. But then the dehydrated 'skin' should more properly be considered as a different phase of material with it's own physical properties, as opposed to a simple dividing surface.
 

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