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### Challenge Questions

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# Lake Surface: Newsletter Challenge (07/19/05)

Posted July 19, 2005 7:00 AM

The question as it appears in the 07/19 edition of Specs & Techs from GlobalSpec:

You and the family are up at the lake house for a vacation. One evening, you're all sitting by the lake, enjoying a little peaceful bonding time. Remarkably, everyone is getting along so when it begins to rain, you try not to let it ruin the moment. Your son remarks, "Hey, Dad, look at those bugs walking on the lake. How can they can stay there on the surface and not be dunked by the raindrops?" What's your answer?

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Power-User

Join Date: Feb 2005
Posts: 264
#1

### Rain Dunking Bugs

07/19/2005 8:18 AM

Since we are talking about a summer storm with the big heavy raindrops the answer probably falls in the realm of probability and chance. The boy is perhaps observing water walkers which use surface tension properties of water to stay afloat (a completely different question). Yes, a direct hit would most likely take out the bug, but because the drops are distributed quite a bit a part in a bugs world, there is a high likelihood that save for glancing blows, Mr. Water Walker will be missed.

Participant

Join Date: Jul 2005
Posts: 1
#2

### Re:Rain Dunking Bugs

07/20/2005 1:17 PM

Paddy, I don't think probability and chance comes into play here. It has to do with the ole' bugs ability to repel water and to use the surface tension of the water to stay afloat.

Friend of CR4

Join Date: Dec 2004
Posts: 1995
#3

08/02/2005 1:23 PM

As written in the 7/26 issue of Specs & Techs from GlobalSpec:

This one is very interesting. Most people think that water striders (those bugs you often see on water surfaces outdoors) are making use of water surface tension effects to stay on the water's surface, and to a certain extent that's true, but recent research indicates that microscopic hairs cover the striders' legs and trap tiny air bubbles that provide tremendous buoyancy and allows them to float. Microscopic images of the legs show tiny hair-like structures called microsetae which are less than 3 micrometers across (a human hair is 80-100 microns, so they're really small). These structures themselves have structure — nano-grooves scored into them that are measured in nanometers (billionths of a meter) in size. Air gets trapped in the micro hairs and nano-grooves and stays in place when the striders are on water, providing a buoyancy that helps support their weight. There's a nice description of this here.

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