Simple Fahrenheit-Celsius Conversion Tip

Editor,

Here's a super simple conversion for room temperature range:

Write out these two sequences:

15 20 25 30 35 (C)

59 68 77 86 95 (F)

Note that the second sequence has the same digits both directions and the first is merely counting by fives from 15.

This is an easy way to convert and estimate Celsius temperatures from weather reports given in Fahrenheit or vice-versa.

Tom Dowling

Reverse Feynman Sprinkler

Editor,

This is similar to an ordinary rotating sprinkler submerged in water and powered by a reverse flow of water.  It led me to consider not just the answer to the puzzle, but how individuals take different approaches to solving it.

One approach is to "look up the answer."  Surely with all the resources of the Internet, one ought to be able to find the specific answer to this problem.  Usually such an approach leads to sources with varying degrees of credibility, and these sources may contradict each other.

Another approach is to trust one's raw intuition.  Here one would perhaps posit that "the sprinkler has to run backwards because the water is going the opposite direction."  But intuition can easily lead one astray.

A third approach is to consider the problem in terms of trusted equations of motion, control volumes, material balances and Newton's laws of motion.  A theoretician may dwell on this approach and consider the problem solved when he/she has a rigorous mathematical proof of the result.

A final approach is the empirical method.  Here one puts the greatest energy into performing an experiment or building a model to test the hypothesis. My idea of good science is an appropriate balance of all four of these approaches.

I didn't have the energy and time to follow Allan's model, so I conceived of a simple kitchen experiment that would perhaps suggest the right answer. I found a large diameter drinking straw with an  adjustable top so I was able bend the end to a 90 degree angle. Then I put the long straight end loosely in my mouth and let the straw dangle downward. I then watched the movements of the straw as I inhaled or exhaled. I definitely did not observe what I expected to observe.

Next, I decided to modify the open dangling end by taping some heavy paper onto the opening so that it was nearly air tight. Then I pierced the paper with a small paper clip so there was a small hole in what was essentially a membrane. I repeated the experiment by blowing and inhaling air through the straw as it dangled. The result was different from that without the membrane. (In case you try to duplicate this experiment, I suspect that it will work best with a large diameter straw rather than a very small one.) 

I was able to create a pendulum action of the dangling straw by either blowing or inhaling in the right rhythm. Now it is possible that some inadvertent movements of my lips caused the dangling straw to do what it did, but I don't think so. I think that the dangling straw is completely analogous to the "Reverse Feynman Sprinkler," and I intend to scratch out some equations to see what I can come up with.

Ronald Leemhuis, MD


Help Needed for a Magnetic Field Project

Editor,

Dean asked about a source for mumetal.

I use mumetal for shielding on photomultiplier tubes when I build scintillators. Its is basically non magnetic stainless steel that's at least 80% nickel. Its never cheap.

Click here for a great deal of information about mumetal.

Here is a sample supplier: http://www.lessemf.com/mag-shld.html

Good luck and please keep us updated on your project.

Tracy Albert

More About Help Needed for a Magnetic Field Project

Editor,

I would love to help Dean. But there is not a lot to go on in his request [for permalloy and mumetal].

One suggestion would be to purchase a kit from one of the magnetic shield companies, like this one.

This kit has a different material than Dean is asking about but it is a good hi perm material.

Jim Hannon

Progress Report on Growing Broccoli in Soil Treated with Gray Water Containing Chlorine Bleach

Editor:

This is a followup to my earlier letter on growing garden vegetables in soil treated with gray water.

The accompanying photo (Fig. 1) shows broccoli 40 days after treating soil with chlorine bleach in laundry water 24 hours before planting.

Figure 1. Broccoli growing from soil treated with laundry water containing chlorine bleach.

Laundry water may reduce weeds, pests and plant diseases in gardens, while reducing the amount of chlorine entering whale habitat, where chlorine kills beneficial plankton in the whale food chain.

I recently reported this experiment to a meeting of ENVVEST, comprising members of US EPA, Washington State Department of Ecology and the US Navy.

Glen Hemerick

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