Wednesday, August 24, 2011

Thorium Nuclear Power questions


We were pleased to get this question because we had just read an article about it. One of the challenges with thorium for reactor fuel is that it has been historically very expensive, monetarily and environmentally, to process. There is a project at LANL that has taken on thorium chemistry. It is called Th-ING, Thorium Is Now Green. This team has developed a much cleaner and much cheaper way to process thorium that avoids exotic chemistry, high temperatures, etc. It sounds very promising. There is a technical article about Th-ING at: http://www.lanl.gov/science/NSS/issue2_2011/story6full.shtml .

By the way, another development happening here is a program experimenting with sandwiches of materials with atom-thick layers of, for example, copper and niobium, that results in a sheet with not only extraordinary strength, but an ability to repair itself, or heal, from radiation damage. These materials may one day serve to shield or replace materials used in nuclear reactors today that become brittle with continued exposure to radiation.

Friday, August 12, 2011

"Work" and the scale of atoms

The word “work,” in physics has a special meaning, and is, as you said, defined as force multiplied by distance. Yes, if the object we are working on doesn’t move, we are not doing any work. This goes against the normal every day usage of the concept work. I sat all day today working at my computer, but I did very little physical “work.” There are a number of words that can get us tangled up like this. There is a wonderful glossary of misused science terms at http://www.lhup.edu/~dsimanek/scenario/physlang.htm

About things the size of atoms. An atom is less than one ten-billionth of a meter across. (Squeeze a meter stick into a millimeter on a second meter stick, and then squeeze the second meter stick into another millimeter, and the smallest meter stick can measure ten or twenty atoms across one of its millimeters!) If an atom were the size of a big football stadium, a proton or a neutron would be about the size of a tennis ball an entire nucleus may be the size of a soccer ball. At that scale an electron would still be nearly invisible, maybe actually invisible, but in any case still incredibly tiny. As I understand it, the strings people talk about in “string theory” are about as much smaller than an electron as the electron is smaller than the atom. Atoms are too small to see with light, so it is small wonder (ahem) that we have no direct evidence of strings.

Technology advances, though, and each step along the way, every lesson we learn, every question we ask opens up a world of new mysteries. The string theorists hope that the Large Hadron (Protons and neutrons are hadrons.) Collider in Switzerland and France will lead them to data confirming or at least supporting the theory. It is good to know there will still be questions and more bigger machines to build after the LHC is running. :-)

Nano Jump-To-The-Moon

Our nano jump to the moon was based on these calculations:

The Moon is about 250,000 miles away (A quarter of a million miles.) A mile has 5280 feet in it. A foot is made of twelve inches. At this point, if we multiply all these numbers together, we will discover that the distance to the moon is (approximately) 15,840,000,000 inches from Earth. One billionth of that would be 15.84 inches or about 15 13/16 inches on a yardstick.

To make this “high” jump, I used PVC pipe, probably 3/4” but it doesn’t really matter, I cut two lengths 15 3/4” long, my cross bar is a piece of 1/16” fiberglass rod about a foot long, and the bases are crossed pieces of 2 X 2 lumber a couple of inches long. I got the rod from McMaster-Carr, my very favorite materials catalog (Google it), but any similar material will work, I wanted to make sure that there was no possibility it would trip or catch a child, and that it wouldn’t break easily or hurt them if someone fell on it. (and I had some lying around.)

I am particularly proud of having thought of marking off 3/4” ticks across the bar, putting it in my drill on low speed, and using a red Sharpie to make the stripes!

I hope this helps you, it has been a popular part of our program.

Online Card Trick Spoiler

Regarding a cute online card trick:
http://www.quizyourprofile.com/guessyournumber.swf

This is wonderful! Thank you Mary Ellen for showing it to me. I DO know how it works but it is so well executed that I am almost reluctant to explain it. If you want it to stay mysterious, leave this entry now!

The trick is that they have added great red herrings, where you pick the color or the crystal ball or the door while you say your number a couple of times in you mind. This has nothing to do with the trick. The trick is like the classic twenty-one cards in three rows of seven trick. We start here with twenty-five numbers, and the program asks us which of five colors it is. This narrows us down to only five numbers. Then it distracts us while we choose a color which has nothing to do with the trick. Next it asks us which house our number is in, with six numbers in each of five houses.

Remember the first question? Well each house has exactly one number from each of the original color groups (Plus five extras added for smoke-screen.) They are all colored alike in the houses, further concealing the process. Giving this information tells the program which of the first five numbers we chose, and for all intents and purposes the trick has been executed. The rest is just distraction. Any door you open at the end will have your number.

What I find fascinating is that the computer can take advantage of my mind thinking of the numbers as physical entities as if they were printed on cards. For example, I can see my brain thinking, as I pick a door, that only one door can have “18” behind it.  The number on the screen, however, is an imaginary electronic construct with no physical reality, in fact it doesn’t even exist until the door opens, so my wonder that the number actually is “18” is my own darned fault. Schrodinger would be proud!

One other thing is that unlike a carbon and water based magician, who might struggle to remember in the first stage which five numbers are red, which are purple, etc. this is the easiest thing to accomplish for a computer program. One could construct a set of cards that would do the manipulations mechanically, but it would be nowhere near as invisible as the computer program.

Durable Hand Generators

We build hand generators from DC gear motors which we find on surplus electroncs websites.  Look for DC gear motors and order a small selection of different ones to test. These are surplus and always change, so if you find one that you really like, buy a bunch. While you are at the electronics store you may want to pick up a pair of large alligator clips and about 18 inches of lamp cord (Two strand wire) per generator.

We get our crank handles from Reid Supply, 3.5” aluminum cranks, the part number is something like CH-35AL (pretty obvious how they coded that!) These don’t have holes in them so they fit any motor shaft size.

 We drill a blind hole (not all the way through) in the handle and fasten it to the motor shaft with epoxy. If we can, we open the motor case and solder the heavier cord directly to the connectors. If we can’t, we will solder the wires together, either way we provide some form of strain relief. we have glued the motors into PVC pipe with the cord knotted and passing through an end cap. Sometimes we have to grind off a metal flange to make a motor more hand-friendly. The alligator clips are soldered to the ends of the wire. We try to keep the wires and the colors of the clips polarized the same way so that saying, “Let’s try connecting all the red clips together” almost has a predictable result. (It depends which way the student turns the crank.)

These generators last a long time, we don’t ever strip the gears in them, and the cost of parts is less than $20. The epoxy joint is typically the failure point and very easily repaired.

We use our generators mostly to turn other generators. Students love it. We have been tempted to make some winches, with pulleys instead of cranks to see if we can lift stuff, and if we can turn the generator with falling weight. Two pulleys on the shaft; a big one and a small one? We have seen a similar device used to split water with electrolysis to make little hydrogen-oxygen explosions. Cool!

Wednesday, August 10, 2011

How Do Eyes Work?


Eyes are very complicated. They have a lot of different parts, and all of the parts are important. You might have to explain this to a grown-up so they can understand how eyes work.

Let's start with light. Light bounces off things and some of it goes through the pupils in our eyes. Those are the little black circles. 

Then it passes through a lens which bends it and focuses the light on our retina, which is a thin tissue at the back of the eye. Focusing means that light from one part of what we are looking at goes to one place on the retina.

Just like the rest of your body, the retina is made up of tiny cells.
These are too little to see without a microscope. The cells in your retina are special because they make chemicals called dyes. When light hits the dyes, the dyes get bleached out, the chemicals break down. You can see this effect with colored construction paper if you put a piece in a sunny window  and cover part of it with something light doesn't go through. After several days or a week, you will see the sunny part has faded. Your eye cells work MUCH faster. Your cells keep track of the dyes, and as they replace the worn out ones, they send a message to your brain about the light that has hit them.

Your brain puts together all the information it gets from all the cells in your retina to figure out what you are seeing. It is a truly amazing process.