# Siphon on the Moon?

**URL:** <https://boards.straightdope.com/t/siphon-on-the-moon/48603>\
**Category:** Cecil's Columns/Staff Reports\
**Created:** [January 5, 2001, 6:24pm UTC](https://boards.straightdope.com/t/siphon-on-the-moon/48603 "2001-01-05T18:24:32Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Burning\_Frog](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@Burning\_Frog](https://boards.straightdope.com/u/Burning_Frog)\
**Post date:** [January 5, 2001, 6:24pm UTC](https://boards.straightdope.com/t/siphon-on-the-moon/48603/1 "2001-01-05T18:24:32Z")

</div>

Siphon on the Moon?

OK, I’m visualizing Cecil’s siphon working on the Moon,  
minus the cat and the fish. So, if someone poked  
a hole with an icepick in the top of the bend,  
it would “break” the siphon just like on Earth?  
Why? Because the hole somehow affects the  
water’s cohesiveness? I’m skeptical.

Alternatively, it would not “break” the siphon at  
all, because the water has so much cohesiveness?  
Then why do siphons “break” on Earth?

Why can’t we make “water boogers?” I was taught  
that capillary action can draw water to the top of  
trees because of water’s adhesion to the walls of  
capillary tubes (it forms a concave meniscus) and  
not because of any special tensile strength.

When a water siphon stops flowing at 34 feet  
(equal to sea level atmospheric pressure) the  
two arms of the siphon look to me very much like  
water barometers. Apparently “Uncle Al” Schwartz,  
the “Usenet physics adept,” regards this as a  
curious coincidence. I’m skeptical.

This reminds me of a story that went around during  
the 1979 gasoline shortage, about somebody trying  
to siphon gas out of an RV and opening the wrong cap.  
Better smell that thing before you suck on it,  
because I think it’s full of crap.

When Al Schwartz “insisted that water’s tensile  
strength remained the conservative explanation”  
it didn’t add any credibility for me. Maybe it’s  
because I live in Berkeley, but that phrase often  
signals me to expect a face full of… uh, highly  
implausible stuff, like “impurities and dissolved  
gases” that reduce the tensile strength of water  
to “the atmospheric case” – except when the siphon  
is working, it which case the tensile strength  
comes back, apparently.

I’ve read this particular column repeatedly, but  
I cannot understand why Cecil “felt entitled to  
call this argument a draw.” I’d appreciate a little  
more explanation.

---

<div class="post-metadata">

**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\
**Post date:** [January 5, 2001, 10:50pm UTC](https://boards.straightdope.com/t/siphon-on-the-moon/48603/2 "2001-01-05T22:50:48Z")

</div>

Burning Frog said:

> [@](#):
>
> I was taught that capillary action can draw water to the top of trees because of water’s adhesion to the walls of capillary tubes (it forms a concave meniscus) and not because of any special tensile strength.

I think it’s a little of both. The capillary action is the adhesion of the water molecules to the tube molecules, but the surface tension (aka tensile strength) is what keeps the water holding to itself, and allows it to flow up. That’s why the limit of capillary action is the size of the capillary - too large a cross section and the required strenght to hold the water together exceeds the tensile strength of the surface tension. Water won’t climb the walls unless it can form the meniscus - it won’t walk up a flat wall in a sheet.

You might also check out this thread also on siphoning:  
[http://boards.straightdope.com/sdmb/showthread.php?threadid=54028](http://boards.straightdope.com/sdmb/showthread.php?threadid=54028)

---

<div class="post-metadata">

**Author:** ![Arnold\_Winkelried](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@Arnold\_Winkelried](https://boards.straightdope.com/u/Arnold_Winkelried)\
**Post date:** [January 5, 2001, 11:40pm UTC](https://boards.straightdope.com/t/siphon-on-the-moon/48603/3 "2001-01-05T23:40:21Z")

</div>

Welcome to the SDMB, and thank you for posting your comment.  
Please include a link to Cecil’s column if it’s on the straight dope web site.  
To include a link, it can be as simple as including the web page location in your post (make sure there is a space **before** and **after** the text of the URL).

Cecil’s column can be found on-line at this link:  
[How does a siphon work? (05-Jan-2001)](http://www.straightdope.com/columns/010105.html)

* * *

moderator, «[**Comments on Cecil’s Columns**](http://boards.straightdope.com/sdmb/forumdisplay.php?forumid=1)»