# What is the "underside" of a water surface with surface tension? Because I saw a shrimp walk on it. **URL:** \ **Category:** Factual Questions\ **Created:** [September 4, 2015, 3:17pm UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907 "2015-09-04T15:17:16Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 4, 2015, 3:17pm UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907/1 "2015-09-04T15:17:16Z")
You know those insects, or amphibians (do I know) who trot around a pond by some combination of weight, weight distribution, and surface tension? Well I was shown, and think I saw–I basically nodded to be polite, and because I thought it was cool–a type of shrimp in an aquarium (a “cleaner shrimp?”) padding around upside down inverted on the surface of the water. How the heck does that work? ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [September 4, 2015, 3:21pm UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907/2 "2015-09-04T15:21:14Z")
Oh that’s interesting. Don’t know how that works and am interested too. I wonder if there are images of this phenomenon. I didn’t find any in a quick search. ---
**Author:** ![Disheavel](https://avatars.discourse-cdn.com/v4/letter/d/e274bd/32.png) [@Disheavel](https://boards.straightdope.com/u/Disheavel)\ **Post date:** [September 4, 2015, 6:50pm UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907/3 "2015-09-04T18:50:30Z")
Why isn’t it simply water tension? I think it is the equivalent of bubbles sitting on the surface of water. There is a force pushing up against the water surface (bubble, shrimp leg) but the force isn’t strong enough to break the surface and release the strain yet. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [September 5, 2015, 11:55am UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907/4 "2015-09-05T11:55:48Z")
The surface forms a web, like a net… a skin… … repulsion is due to hydrophobic molecules on the surface of the insect … which can add to surface tension effects. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 5, 2015, 12:05pm UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907/5 "2015-09-05T12:05:28Z")
I suspect it’s just surface tension redux. Surface tension happens with water because the liquid sticks to itself fairly strongly due to hydrogen bonding. So when you have a sheet of water, “breaking through” that sheet takes a force that exceeds the tendency of water to stick to itself and exclude the intruding object. Anyways, this would happen the other direction as well. Surfacing, you are trying to break that surface water has formed by sticking to itself. If the shrimp is very slightly positively buoyant - the force of buoyancy is just slightly above the mass\*g (weight) of the shrimp - it wouldn’t break through the surface. Also, the hairs on an insect leg enormously increase it’s surface area with respect to the water surface, boosting the effect of this force probably hundreds of times. ---
**Author:** ![Myglaren](https://avatars.discourse-cdn.com/v4/letter/m/f1d935/32.png) [@Myglaren](https://boards.straightdope.com/u/Myglaren)\ **Post date:** [September 5, 2015, 12:26pm UTC](https://boards.straightdope.com/t/what-is-the-underside-of-a-water-surface-with-surface-tension-because-i-saw-a-shrimp-walk-on-it/729907/6 "2015-09-05T12:26:50Z")
[YouTube](https://www.youtube.com/watch?v=Tu9J9Lo0oc8)