# Gas station without pumps

## 2012 April 30

### California State Science Fair 2012

Filed under: Science fair — gasstationwithoutpumps @ 22:25
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I spent this morning working as a volunteer for the Display Approval Committee for the California State Science Fair.  I did not have to disapprove any posters, though I did ask one student to remove the samples of decaying leaves and compost from his display.

In the afternoon, I looked at some of the high-school posters with my son.  One thing that CSSF did new this year was to have students stand with their posters 3:00–4:30 p.m. for public viewing.  This was great, as it gave the public (including me) a chance to hear some of the spiels.  I mainly listened to kids in the high-school Mathematics and Software category (the category my son is also in).  There were some pretty impressive posters and presentations—the category has become a tough one (like biochem has been for a few years).

I did notice that some projects or topics appeared in different categories.  For example, microbial fuel cells could have ended up in microbiology, chemistry, environmental science, or electricity and electromagnetism.  Bioinformatics projects ended up in either math and software or any of several biology categories.  I think that it would be a good idea for the judges to get together and make some more detailed categorization examples, so that all the microbial fuel cells end up in the same category, for example.

After the public viewing, they had the keynote speech.  For the second year in a row they got an incompetent public speaker, chosen apparently for her connection with the fund-raising arm of the science fair.  Last year they had Gary K. Michelson, who talked like an actor playing the part of a scientist, refusing to talk at all about science.  This year’s speaker, Cheryl Mae Craft, was like a parody of an academic speaker (including the contentless pie chart slides and slides automatically advancing past the point she wanted them to and her unable either to roll them back or recover from the mishap.  This being Los Angeles, one almost suspects that they were hiring out-of-work actors to play the parts of the keynote speakers.

Both years the speakers studiously avoiding talking about science at all (to an audience consisting primarily of students who were passionate about science).  I believe that Dr. Craft had one slide about her science, then told students to look her up on the web.  If Dr. Craft had a beard, she could have been Prof. Smith:

I do remember that a few years ago they had some good keynote speakers, so it isn’t as if CSSF was incapable of finding them.  I suspect that some idiot on the CSSF board selected fund-raising luminaries (without paying attention to whether they could give a good speech), and then hamstrung them by insisting that they not talk about science.

I believe that the audience would have been much better served if  scientists talked about their work and not about vague platitudes.  I’d rather listen to a meaty talk which I only understand a quarter of, than a contentless one like the last two keynotes.  If you want to inspire kids to go into science, don’t put examples of “successful” people who sound as boring as paper pushers and who can’t or won’t talk about science (perhaps they are now purely administrators and don’t do science any more?). It seemed like the keynote speakers were chosen for political payback, not for the benefit of the audience.

It would be better to get an unknown scientist doing exciting work and have them talk about that work as if it were the most exciting thing in the world.  I’m sure that there are hundreds of scientists in LA who could have given a better keynote, and 1000s in California.  Hell, having the winners from the previous year’s science fair talk about their projects would have been much more interesting and inspiring.  That would be a keynote that would inspire kids!

## 2012 April 29

### Tuition scholarships for Modeling Instruction Workshops

Filed under: Uncategorized — gasstationwithoutpumps @ 13:11
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This short post is just to pass along the news that there are 35 tuition scholarships available for high-school science teachers to attend one of the ASU modeling-instruction workshops this summer.  More information at Great News: Tuition Scholarships for Modeling Instruction Workshops | Action-Reaction and about the workshops themselves at http://modeling.asu.edu/MNS/MNS.html

Note: I’m just passing on this information—I know nothing more about it than what I have posted here.

## 2012 April 28

### Nonsense advice from a principal

Filed under: Uncategorized — gasstationwithoutpumps @ 09:37
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The principal of the campus where my son’s home-school umbrella school is located just sent around an e-mail message about a rather disturbing incident (I’ve removed the names of the people and locations):

On Monday, April 23rd at 4:00 PM, a student was walking home from school.   As she walked past P_ Street on S_ Ave, a man on a green, rusty beach cruiser began following the student.  The student ignored the man who continued to follow her and say inappropriate comments all the way up until she reached her front door.  The student’s parents were home and S_ C_ Police were called.  The man, C_ H_, was arrested and jailed.  The police are investigating this incident and are asking others who might have had a similar experience contact them and report the incident to them.

That was useful, if somewhat disturbing, information—I appreciate the principal letting parents know, rather than waiting for us to read about it in the newspaper.  This is a town with a lot of transients, tourists, homeless people, and drug users, some of whom have mental problems, so incidents like this one are not rare. (Note: I am not equating the 4 groups of people, listed, nor claiming that C_ H_ belonged to any of them. I’m just pointing out that our small city is not a place where everyone knows everyone, and that “stranger danger” does exist here.)

Unfortunately, rather than praising the student and the parents for handling the situation in the best possible way, the principal went on to give some really senseless advice:

Please consider these guidelines in an effort to avoid any future situations:

• Immediately call 911 whenever you are approached by anyone that you do not know.
• Always let people know where you are when you are going anywhere by yourself
• Travel in groups whenever possible; there is safety in numbers
• Elementary students should not travel to and from school alone
• Do not interact with strangers

The middle three pieces of advice are reasonable: someone should know where students are, particularly when they are traveling alone, and elementary school students (younger than about 9 years old) should probably not wander our city alone.  Being with a buddy is a sensible precaution against ordinary dangers like getting lost or twisting an ankle, as well as the much rarer stranger danger.  Some neighborhoods are fine for kids as young as 6 to wander alone, but the most attractive places for kids (like the beach) are also the most dangerous.

The first and last pieces of advice are not suitable as advice to children, because they are too absolutist and extreme. Consider the situation of a new student at school—they don’t know any one and no one knows them.  If anyone approaches them, they are to call 911.  If they approach anyone, then that person is to call 911. The poor kid can’t win, no matter what they do, if they follow the principal’s simplistic advice.  Even worse, if kids actually followed this advice, the 911 number would be flooded with calls, and the kids would probably be arrested for tying up the line with non-emergency calls.

The last piece of advice is vaguer than the first one, since neither “interacting” nor “stranger” is defined.  If taken literally, it is almost as ridiculous as the 911 advice, though, since it provides absolutely no way for a person to change from being a stranger to being a friend.

I’m sure the principal meant well—they usually do—but this sort of ridiculously overstated advice is not something we should seriously offering to teach our children how to be safe.  Always calling 911 whenever anyone you don’t know approaches you is neither reasonable not feasible (many students do not even have phones).  Perhaps it is just as well that this principal is stepping down at the end of the year, though I doubt that we’ll get anyone more reasonable—the job (like most middle-management positions) seems to attract people with small minds who like to make petty rules and enforce them, without thinking through the consequences of bad rule making. The one really good public-school principal I’ve met (who was principal at my son’s first elementary school) retired a few years ago.

What advice should we be giving our kids, so that they are safe now and become competent adults who will continue to be safe?  I think that kids do have to be aware that there is some danger in the world, and that other people (kids or adults) can sometimes be part of that danger, but that fairly simple precautions can reduce the danger to an acceptable level.  The hard part is coming up with the appropriate precautions for kids of different ages and different levels of social skills.  What is appropriate advice for a 6-year-old might be ludicrous for a 16-year-old (and vice versa).  Since the campus involves K–12 students including home-schooled and alternative schools, the age and maturity range for the school is even wider.

Surrounding yourself with people you know and who know you is a common piece of advice, and generally fairly good (the middle 3 of the principal’s list)—unless those people happen to be gang members or meth addicts.  Then you may be better off staying as far from them as you can.

The advice I would have given in a letter like this one from the principal is more restricted and more specific:

• Elementary students should not travel to and from school alone.  Travel with a buddy or with an adult whom you know.
• Let responsible adults (parents or teachers) know where you are going when you are going anywhere by yourself.
• Travel in groups of people you know and trust; there is some safety in numbers.
• If harassed by anyone, try to get away and call 911 as soon as you can, to let the police know.  Try to give the location and a good description of the person, so that the police can identify them. Do not confront the harasser and do not respond to verbal attacks, but defend yourself if attacked physically.

I’m still not really happy with this list, but it was the best I could come up with this morning. (I know that the vocabulary is more appropriate for high school kids than for elementary kids, for example.) Can any of my readers come up with a better succinct list suitable for sending out to parents of a wide range of kids?

## 2012 April 27

### Physics homework chapter 11

Filed under: home school — gasstationwithoutpumps @ 22:10
Tags: , , , ,

Chapter 11 of Matter and Interactions is angular momentum, finishing up the triumvirate of conservation laws (momentum, energy, and angular momentum).

I’ve not come up with any labs to do, and with class cancelled next week I’m not sure when we’ll get to do an angular momentum lab.  Class is cancelled because my son and I will be on the bus back from the Oregon Shakespeare Festival with the rest of his dramatic literature class. We aren’t taking the bus up with the class, since it conflicts with the California State Science Fair, where he is entering in one category and I’m judging in another—we’ll take a red-eye flight from LAX to MFR and a taxi or shuttle to Ashland to catch up with the class. As if he weren’t busy enough, he has three performances of the On the Fringe teen show at Broadway Playhouse this weekend and AP tests when he gets back from Ashland.

Anyway, Chapter 11 homework, which we’ll try to have at least half done by Fri May 11, our next meeting: 11.P.40, 11.P.49, 11.P.50, 11.P.55, 11.P.57, 11.P.63, 11.P.66, 11.P.67, 11.P.75, 11.P.76, 11.P.94.

(Note: typo in 11.P.75: the first ω should be ω0, the initial angular velocity.)

There are some gyroscope labs suggested in 11.P.90 and 11.P.91, so maybe we can try them—read them before class anyway.

### Astro-blaster

Filed under: home school — gasstationwithoutpumps @ 20:49
Tags: , , , , ,

Astro-blaster sold by Arbor Scientific. The bottom three balls have smaller holes, so do not come off the common shaft. The top ball has a large hole and is free to fly off the shaft. Much of the energy of the 120g system is transferred to the 4 top ball, so the little ball goes flying up to the ceiling from even a modest 10" drop

I did have one other toy that we used in today’s class—one I should have had 2 weeks ago when we were doing collisions.  Arbor Scientific calls this toy an Astro-blaster. The idea is simple: you drop the whole unit from a foot or two above the floor, and the little ball goes flying up to the ceiling at high speed.

I had done a crude version of the demo last week using a basketball and a small rubber ball, but neither of them had much bounce to them, and it was hard to keep them vertically aligned, so the demo was not very impressive. This demo unit, with high coefficient-of-restitution balls and the shaft to keep them aligned makes for a much more impressive demo.  I’m not sure why they use 4 balls rather than 2.  Does it make for more efficient energy transfer? Or is it just to keep things aligned more easily?

The balls have diameters 4.8cm, 3.7cm, 2.6cm, and 2.1cm, so should have masses roughly in the ratios 11.9, 5.5, 1.9, 1 (not correcting for the holes drilled in the balls—the total mass is about 120g but the smallest ball is more like 4g than 6g).  We should be able to figure out what happens when the bottom ball hits the floor.  At that point all the balls have the same vertical velocity $-v$ and momentums $-11.9 v, -5.5v, -1.9v, -v$.  The big ball is much less massive than the floor, so (assuming perfect elasticity) rebounds with velocity $v$, immediately colliding with the ball above it.  The momentum of this pair is $(11.9 -5.5)v$ and the energy is $1/2 (11.9+5.5) v^2$.  If we again assume an elastic collision (energy conserved), we can figure out the velocities of both balls after the collision.  Perhaps the easiest way to do this is to change to an inertial reference frame in which the total momentum is 0 (moving upward at $\frac{11.9-5.5}{11.9+5.5}v = 0.368v$).  In this frame the balls are moving toward each other with velocities $0.632v$ and  $-1.368v$, and after the collision will be moving apart with velocities $-0.632v$ and $1.368v$. That means that the second ball will be moving upward at $1.736 v$ with respect to the floor.

Now we have another collision between balls 2 and 3, with the momentum of the pair being $(5.5 * 1.736 - 1.9)v$, so the inertial reference frame in which they have zero momentum moves upward at $\frac{5.5*1.736-1.9}{5.5+1.9}v = 1.034v$.  The balls come together with velocities $0.702v$ and $-2.034v$, so ball 3 ends up moving upward at $(2.034+1.034)v=3.067v$.

The final collision between balls 3 and 4 has combined momentum $(1.9*3.067-1)v$, so the inertial reference frame in which they have zero momentum moves upward at $\frac{1.9*3.067-1}{1.9+1}v=1.665v$.  The balls move together with $1.402v$ and $2.665v$, so the little bounces off with $4.329v$.  That means it leaves with 18.7 times the kinetic energy it came in with, and should bounce to that multiple of the initial height.

What would happen if we used a 19.3 to 1 ratio with just 2 balls?  We’d have an inertial frame moving upward at $\frac{19.3-1}{19.3+1}v=0.901v$ and the small ball would leave at $2.803v$, which is much less impressive than $4.329v$.  So there is good reason to stack many balls.  One could write the equation for the bounce of the final ball, and figure out the optimal ratios of balls to get the maximum bounce with a fixed weight for the final ball and for the total mass.  I tried doing this for 3 balls, with the smallest one being 1 and the total mass being 20.3 (as in this example), and got 15.8, 3.5, 1, which would give $2.275v$ for the middle ball and  $4.094 v$ for the top ball, slightly less than for 4 balls, but I could easily have goofed in doing the algebra, even with the aid of Wolfram Alpha.  I’d have to write a program to do the computation for more balls.  Clearly there is an optimal number of balls to use given the total mass relative to the mass of the smallest ball, since making a string of 20 identical balls would cause an effect like Newton’s cradle, with the top ball only leaving at $v$.  I wonder whether 4 is indeed the optimum for this ratio of masses.

Of course, all the analysis above assumes that the collisions are perfectly elastic, which is nonsense.  The material of the balls provides a high coefficient of restitution, but nowhere near 1 (the closest material I know to that property is “liquidmetal“, which would probably shatter if used in this demo).  I did not measure the coefficient of restitution of the balls (but from my son’s 5th grade science fair project I would estimate it as about 0.86, based on the measurement of similar bouncy balls).  I don’t feel like redoing the analysis with a more realistic coefficient of restitution.  I did determine that dropping the Astro-blaster from 11″ resulted in not hitting the 8′ ceiling, but dropping from 12″ did, so the ratio of heights is between 8 and 8.7, not 18.7.  I wonder whether the Astro-blaster was optimized assuming elastic collisions or the actual coefficient of restitution.

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