Image for reference:

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As can be seen in the above image, whenever my comb comes in contact with water, a little of it is trapped between the teeth. This happens whether I dip it in still water or place it under running water.

  1. Can someone explain what's holding up the water? I think surface tension or capillary action may have something to do with it but not sure how exactly they play out here.
  2. Would the water hold up even if the teeth were completely frictionless? Intuitively answer seems to be no.
  3. Could there be any applications of this phenomenon? I'm seeing that water could be stored at an elevation without continuous supply of any more energy.
  • 2
    $\begingroup$ You can already store water at an elevation without consuming energy - that's what tanks are for. $\endgroup$
    – Al Nejati
    Commented Oct 11, 2018 at 8:47
  • 1
    $\begingroup$ Tausif Hossain used the word, "hydrophilic." Water sticks to hydrophilic surfaces. The opposite is "hydrophobic" (afraid of water). If the comb was made of or coated with a hydrophobic substance, you could hold it under water, but as soon as you pulled it out, it would be completely dry--the water would just slide right off. $\endgroup$ Commented Oct 11, 2018 at 17:04

2 Answers 2


I believe that the force that is keeping those water droplets stationery even when the comb is vertical is the cohesion and adhesion of water molecules as they are attracted to each other (molecules near one teeth to molecules near the other teeth of the comb to form a sort of bridge) and also the attractive forces of sticking to the walls of the teeth of the comb.

I should point out that it is not mechanical friction rather it is intermolecular attractive forces between water molecules and with the molecules in the comb that is making a significant contribution because friction depends on the normal reaction force, $R$ by $F=\mu R$ and for a vertical water column here friction is almost non-existent as the water pressure is so low at such small heights so the horizontal normal reaction force would also be very low making friction very low as well.

So you can see that water could easily be held up even without friction. Consider a simple analogy of a hydrophilic surface(attracted to water) being completely vertical(so no normal reaction force and no friction) and a water droplet will stick to the surface and not fall down due to the intermolecular forces with the surface. This can even occur when you have a drop of water stuck to the tip of your finger and held vertically and it doesn't fall(without friction once again as it is vertically placed) due to cohesive and adhesive forces.


seem to be the adhesion force between teeth of comb and water and cohesion force are capable to maintain the weight of that water against gravity. if the gap between teeth is large that the adhesion and cohesion forces cannot hold the weight of water between, water would always fall down.


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