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Author Topic: Why do fluids in freefall seperate and 'globulise'?  (Read 1620 times)

Offline krytie75

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Whenever you see slow motion video of liquids falling, they quickly break apart into many small droplets.  I was wondering why this happens, considering that whatever is causing it is strong enough to go against the surface tension of the fluid, which I would have thought would 'prefer' the fluid to remain as one larger entity.

N.B. this only seems to be the case when the fluid is falling relative to the atmosphere it's falling in.  Fluids in free fall where the atmosphere is falling at the same rate as the fluid (i.e onboard an orbiting space shuttle), remain in the most part as larger 'globules'.


 

Offline Soul Surfer

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Why do fluids in freefall seperate and 'globulise'?
« Reply #1 on: 30/03/2010 00:03:23 »
Surface tension stabilisation gets weaker as the globule size increases because the pressure due to surface tension increases as the curvature of the surface increases i.e. smaller drops have higher pressures inside them (see the topics on pressure inside bubbles and balloons for a more detailed explanation).  Terminal velocity when falling through the air increases as globule size increases.  As a large blob of fluid accelerates towards its terminal velocity the effect of air resistance causes the drop to flatten until it becomes unstable under its surface tension and breaks up into smaller globules.

These processes determine the limiting sizes for raindrops which tend to grow by accretion and then break up as the fall through a rain cloud.

 

Offline krytie75

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Why do fluids in freefall seperate and 'globulise'?
« Reply #2 on: 30/03/2010 00:24:12 »
Perfect answer.  Many thanks!
 

Offline syhprum

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Why do fluids in freefall seperate and 'globulise'?
« Reply #3 on: 30/03/2010 20:29:33 »
My Son in Brisbane complains that they sometimes get tennis ball sized hail stones !.
 

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Why do fluids in freefall seperate and 'globulise'?
« Reply #3 on: 30/03/2010 20:29:33 »

 

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