Ask Mr. Science
page 22

 
arrow left arrow up arrow right
prev page
 
index
 
next page
 

 

Tornadoes

[Also see: Weather, and fog in a bottle]
To make a tornado, you need a few ingredients: (1) a strong updraft (2) something to start the rotating action and (3) plenty of available energy. In the summer in the central US, warm moist air flows up from the gulf of Mexico. At the same time, colder air flows from the North, and slides over the top of the warm air. Warm air at the bottom, cold air on top - this is not stable. So masses of warm air rise, and these upward surges can turn into massive thunderstorms. So here we have the strong updrafts. Where the air masses slide over each other, tubes of rolling air can form, as the air on top goes in one direction, and the air below goes in the opposite direction. When such a tube of rolling air gets caught in an updraft, one end can be pulled up, and the other end can descend below the bottom of the tunderstorm cloud. In the photo on the right (from here), you can see both: a tornado descending, and a rolling tube.


These conditions are most common in the areas shown in dark colors on this map (from here). Notice that mountains, both in the east and the west, break up this inverted layering, and therfore there are no tornados where we live, in Santa Fe, NM.
To explain things, I made a tornado machine to show that rising air, combined with some rotation, will self-organize into a vortex, which on a small of course scale looks more like a tornado than a hurricane. The tornado in the box is 4 feet tall.

Bigger

Here is an interesting observation: look at the water in the pie pan when there is no dry ice. The tornado is still there, but you can't see it. However, the pressure in the center of the tornado where it touches the surface of the water is so low that it raises a small dimple one the surface to a height of 2-3 mm. This bump of water scoots around the surface. I made a movie of it here. In the clip, you can see the bump, and dust in and on the water slowly turning. I break up the vortex with my hand, and you see it re-establish itself quickly.
Bigger

Links:
In the Exploratorium in San Francisco, there is a large tornado box. There is a big fan on top sucking air upwards, and a vapor maker under the floor grating, but nothing to start the air turning. You have to step up into it, and run around until the tornado forms. How cool is that!

Bring:
  • Tornado box (plus tube)
  • Box fan
  • Lights
  • (grounded) extension cord
  • Dry ice, gloves, hammer
  • Pie pan
  • Tape, rubber bands
  • Cooler with extra insulation
.. and for stand-alone
  • Water boiler
  • Large water container
  • Funnel
  • 3-way grounded splitter



yearly since 2005
 

Hurricanes

[Also see: Weather, and fog in a bottle]
The year 2005 had the most extreme hurricane season on record, with Katrina devatating New Orleans, and the National Hurrican Center running out of names, the first hurricane in history hitting Spain and Portugal, and hurricane Epsilon still active past the official end of the hurricane season. Naturally there were some questions about hurricanes.

The second thing to explain is why hurricanes rotate in the first place, and why they go counterclockwise in the Northern Hemispere and clockwise in the Southern hemispere. For this purpose I made a flat rotating earth (hey, if Intelligent Design can be called 'science', I can claim that the earth is flat), so that I could show that a rolling ball on a rotating disk does not follow a straight ground path, but curves to the right in the Northern hemisphere. Here's how to make this turntable.

2005, Feb 2011
 

How does the VLA work?

The Very Large Array is located not too far from here (on Google Earth go to 34°04'32.85"N 107°36'35.83"W), so I was asked about it. Besides explaining simple parabolic mirrors, I wanted to make 2 points: 1) why are they so big, and 2) why do you chain them together?
I made a parabolic shape out of a piece of aluminum flashing (30x12 cm or so), and some cardboard. You can see a cork in the focal point. Off to the right out of the picture is a lamp (same one I used for the soap bubbles). You can see the light rays converging and lighting up the cork. In addition, I had a laser pointer, you can also see the reflected laser light.
All the light that fall on the mirror gets collected in the focal point, and that

 

meerkats on the lookout February 98: Where do all the animals come from? Time for a break from all the space stuff. There had been some other vague questions about animals and plants, so here was an opportunity to talk about evolution, one of the great pillars of science that the kids should be familiar with.
I decided to make up a game that could be played in class that would show evolutionary pressure, drift, divergence and all that good stuff. Here is how it went:

First I set the scene: We have a small green valley, with brush, trees and grass, all drawn on the board, and we are going to play at being these medium-sized herbivores. They live for 4 years, then they die.
To make it easier for the children to keep track of their 'age', I folded colored sheets in four, and marked quarters with large numbers 1-4, so that they could fold the right number out. Each 'live' animal gets to hold one.
In the first phase of the game, we're basically going to populate the imaginary valley up to the limit of the food supply, and follow the population for a while. Each time we turn over a year, all live animals turn a year older, and get to multiply - that is, pick another kid to join the herd, who starts off at age 1. Those who turn 5, die and leave the herd. The valley can support 14 (that's how many age-cards I made). Of course it takes only 4 generations to saturate the food supply, after which the new-member rate equals the death rate. This gets pretty boring after a few rounds, but it shows that a population will fill an unoccupied environmental niche, and then becomes resource-limited.
In the next phase, we're going to throw in some random variation. In addition to the age-cards, I had made up 14 simple tape measures
Colored 8.5x11 sheets from the recycling, cut into 4 lengthwise strips. Tape 7 different colored strips end-to-end, fold them up and hold them together with a clothes pin. Unfold as many strips as you need 'feet', and put the clothespin back on the rest.
The 'live' animals each get a tape measure so they can keep track of how tall they are. They all start out at 3', so they can eat the shrubbery, but cannot reach the leaves on the trees. Now, every time someone gets to pick an offspring, they get to roll a die; I had some 8-sided dice, and made the following assignments:
  • throw 1-2: offspring is 1' shorter than the parent
  • throw 3-6: offspring is the same length as the parent
  • throw 7-8: offspring is 1' taller than the parent
After a few rounds/years, the population is still mostly 3', but there are now a few tall and short members.

Then evolutionary pressure strikes: the climate in our little valley changes, and it turns into a a plain with a little grass and trees, but no more brush. There is not enough food for the medium-sized brush eaters, and they die off. The taller animals get to munch on the trees, and a few of the smallest animals get to survive on the grass. After a few rounds/years/generations it becomes clear that we now have two different types of animals where we started with one type. Just throwing the dice and some environmental pressure led to emergence of new species. That's just about all we got done in one hour.

The next week, I reviewed the game, and put the proper names to various things we had done. While we were playing the game the week before, I had had no time to introduce the terminology ('evolution', 'survival of the fittest' etc.), or any of the names (Darwin, Wallace). By coincidence, I had just received the Feb 98 issue of Scientific American, in which there was an article about the emergence of antibiotic resistance - a prime example of evolution in real-time action in our world, and I used that to stress that evolution is not just a thing of the past. Also, that under current circumstances, that the human race can no longer evolve.

Of course, while we were on the subject, I had to mention DNA, stepping down in scale from my fingertip to cells, then nuclei and finally DNA. I had made up some new covers for a set of paperback books of various thicknesses, a fat one titled 'How to make a Person', an equally thick volume 'How to make a Monkey', a thinner one 'How to make a Frog, and a single sheet titled 'How to make Bacteria'. These codebooks are supposed to be written with only the letters C,G,T and A. Another important point about these codebooks is that they contain many almost identical chapters and pages between them, even between the 'Person' code and the 'Bacteria' code. (Feb 16 98)








Suggestions, comments, greetings are greatly appreciated.
Just click here
and type away!

arrow left arrow up arrow right
prev page index next page
Back to my home page