Hydrophilic vs Hydrophobic Sphere
Classical Mechanics
Level
5
If you drop a Hydrophilic and a Hydrophobic sphere of the same size and density (more than water) at the same time into a vessel filled with water, which one will hit the bottom of the vessel first?
Hydrophilic
Hydrophobic
Both at the same time
Depends on Depth of the Vessel
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1 solution
Check out this video from MIT https://www.youtube.com/watch?v=mXaltOAVWL8
(1) At the beginning both the spheres are at the same level.
(2) The moment cavity created by Hydrophobic sphere is broken it travels slowly for few moments and hence for some time the Hydrophilic Sphere is ahead. In my opinion this happens because the loss of momentum on impact with water is greater for the Hydrophobic sphere than for Hydrophilic sphere. You can clearly see a much bigger water splash when the Hydrophobic sphere hits the water surface. The force of the splash will clearly slow down the Hydrophobic sphere more after it hits the surface.
(3) However, within a few moments the Hydrophobic sphere gains momentum and leaves the other sphere behind.
Hence the answer is clearly dependent upon depth of the Vessel itself, if it is too shallow then both will hit the bottom at the same time. If it is slightly deeper then the Hydrophilic sphere will hit the bottom first and if it is very deep then surely the Hydrophobic sphere will hit the bottom first.
Image 1 : Same Depth
Image 2 : Hydrophilic Sphere Ahead
Image 3 : Hydrophobic Sphere Ahead