All posts by Chris

Experiment Sunday update: Electric Circuits

[Note: Each week my geeklet and I have "experiment sunday", a brief and casual exploration of hands-on science and engineering.]

This week’s experiment was a great success. That isn’t to say that it went off without a hitch; the hitches made for more valuable learning than the experiment itself. We set out to make a simple electric circuit, but what we ended up doing was troubleshooting and learning about unstated constraints.

The experiment was a series of steps from The Science Book Of Electricity (Gulliver Books, 1991). The book has a few simple experiments like this one, described in general terms with lots of photos. There’s no theory and not much in the way of details, but the descriptions were enticing enough to catch my eight-year-old geeklet’s interest without any pushing from Dad.

The first step was to make a simple circuit using a light-bulb holder, bulb, two lengths of wire, and a battery. Trivial stuff, we lacked some of the necessary materials. The hardware store had everything we needed, but our parts were lost among all the variations of bulbs and wiring available. (Lesson: a simple parts list contains a lot of assumptions.) We eventually picked out a basic bulb holder, a set of 4W night light bulbs, and three feet of coated copper wire.

On returning home, we set to wiring up the circuit. Stripping the wire was easy with a pair of scissors, but the wire itself was so thick as to be unwieldy. (Lesson: there’s wire, and there’s wire.) With some work, we were able to screw two lengths of wire onto the bulb holder. The geeklet taped one wire end to the negative end of a battery, and I touched the other wire to the positive end. Let there be light? Well, no. (Lesson: it probably won’t work the first time.)

Now came the fun part: troubleshooting! How did our setup differ from the book’s description? The geeklet noticed a caveat in the book: “The battery must be the same voltage as the bulb.” What did that mean, though? The battery’s voltage was printed helpfully on the side: 1.5V. The bulbs, though, were listed as 4W. (Lesson: units are important.) I talked a little bit about the difference between current and voltage, and we looked more closely at the package of bulbs. No hint of voltage listed anywhere. Hmm. A quick check with Mama (who recently had to buy bulbs for one of her projects) yielded the clue we needed: a bulb’s voltage is often listed on its base.

120V. A bit of a difference, then. What to do? Improvise! (Lesson: improvise!)

We scrounged through the tool box to see if there were any other bulbs. We found a krypton bulb for a flashlight, which was listed (now that we knew what to look for) as 3.6V. Closer, but how to make up the difference between a 1.5V battery and a 3.6V light? This gave me a chance to talk about serial vs. parallel circuits, and how batteries in series will add their voltage together. 3 batteries at 1.5V made 4.5V, which should be close enough to make the bulb light up.

The geeklet found and taped together three D cells, which made an impressive battery of batteries. We dropped the krypton bulb into the bulb holder—a loose fit, but it closed the circuit if placed carefully—and wired up the rest again. Let there be light? Yes! (Lesson: persistence pays off.)

The next step was to wire in a pair of thumbtacks, spaced slightly apart on a bit of cardboard. These allowed us to bridge the gap with pins, coins, cloth, buttons, and other things that may or may not carry electric current. A tester! (Lesson: even our improvised monster circuit met the requirements of the experiment.) Once that principle was shown, we used one of the handy current-carriers (a paperclip) to fashion a contact switch. The geeklet showed off the completed circuit and switch to Mama, and we talked about applications like telegraphs and signal lights.

Writing this up, I just now realize that we re-invented the flashlight using (essentially) flashlight parts. Oh well, the process was the important thing.

a note about passwords

Passwords bug me. Specifically, password management on most websites is maddening. Here are a few things to keep in mind when designing yours:

List your password-format rules up front. All too often, sites ask for a password with no indication of their format rules, then scream “ERROR!” when you don’t guess correctly. Yell at your users less by telling them what you want first.

Don’t limit the size of a password unless you absolutely have to. Honestly, it’s 2012. Databases can store unlimited-length strings, and the security of a password is improved by length. If your user wants to use the Gettysburg Address as a password, let them go for it.

Ditto for the content. If the user wants ancient Greek poetry for their password, then don’t freak out about the character set or complain that it doesn’t contain any numbers. Honestly, I once had a health-care provider prevent me from using spaces and punctuation in a password. “Alphanumeric characters only”. Way to be secure, guys.

Don’t limit the password format at all unless a compromised account will damage your service as a whole. No minimum length, no “special characters” requirement, no “at least one number”. I know, this is a tough one to swallow. Take an honest look at the worst a malicious user could do; if the only harmful effects are to the user choosing the password, then let them choose whatever they want.

Rate the strength of a password as the user types, and give hints on how to improve it. If you do this, though, get it right. It’s annoying to type in “correct horse battery staple” and have some out-of-date algorithm tell me it’s “Weak“. It’s worse if the system rejects it outright, but even the knowledge that your algorithm sucks makes me doubt the overall security of your system.

Check that your login fields are friendly to automatic login. I’m more likely to choose a unique password for a site when I can hand off the job of remembering it to my browser or keychain. Each time I have to click “forgot password”, though, my choice is going to be easier to remember (and probably less secure).

watching space stations dance

If you’re in Southern California on January 5th, you might get a chance to see two space stations in the sky at the same time. (Pretty cool, right?)

If it’s clear enough, and if I’ve read the magnitudes and times and directions correctly on Heavens Above, here’s what I’ll be doing that night:

  1. At 5:00pm I’ll go outside and stand in a nice dark spot. (I live in the middle of San Diego, so that takes a few minutes to find.)
  2. At 5:05 I’ll look to the northwest for a bright object moving toward the northeast. If it’s moving slowly and not blinking, it’s the International Space Station. Population: 6. I’ll wave to Daniel, Anton, Anatoli, Oleg, Donald, and André.
  3. At 5:07, when the ISS is as far up as it’ll get in the northeastern sky, I’ll look to the southwest for a dimmer object moving toward the northeast. If it’s moving slowly and not blinking, it’s Tiangong 1, the first part of China’s space station. Population: 0 so far.
  4. Until about 5:10, when Tiangong 1 is right overhead and ISS drops below the eastern horizon, I’ll watch the two of them share the sky.

Thanks to Allan Manangan for passing along the news from David Dickinson on Twitter.

The Mpemba Effect: A Good Case For Citizen Science?

I just read an intriguing article on the Mpemba effect at Skulls in the Stars. Between the history of the effect and the continuing puzzle of what causes it, this is the best example of science-as-a-process I’ve ever seen:

Mpemba made his accidental discovery in Tanzania in 1963, when he was only 13 years old and in secondary school. In spite of widespread disdain from his classmates, he surreptitiously continued experiments on the phenomenon until he had the good fortune in high school to interact with Professor Denis Osborne of the University College Dar es Salaam. Osborne was intrigued, carried out his own experiments, and in 1969 the two published a paper in the journal Physics Education.

So what did Osborne’s research show? He placed a 100 cm³ beaker filled with 70 cm³ of water on a sheet of insulating foam in a freezer, and timed how long it took for the water to freeze. For temperatures up to 20 °C, the time was roughly proportional to the temperature above freezing, up to a maximum of 100 minutes at 20 °C. For higher temperatures, however, the time dropped dramatically, down to 40 minutes for 80 °C water!

Be sure to read the complete article for the whole story, including many attempts to characterize the Mpemba effect over the years. 50 years later there still isn’t a strong consensus about what causes the effect, and in many cases it’s supposed to be difficult to reproduce.

To me, this is crying out for a citizen-science experiment with lots of participants, similar to the way Biocurious works. The experiments themselves are dirt simple (and cheap) to implement; all they really require is water, a heater, and a freezer. The rest is a matter of documenting all the (potentially) relevant variables, including the heater and freezer used, the source of the water, the type of containers, and even the geocoordinates of the experimenter. (Hey, who knows, right?)

A second generation of citizen-science experiments could then be designed based on trends in the first-generation data. The fun thing about this step is that (as Galaxy Zoo has shown) the data often suggests results that weren’t expected before it was being collected. (That shouldn’t be surprising; this is science after all.)

The point of each subsequent generation would be to build more accurate predictions of which experimental setups would or would not produce the Mpemba effect. Eventually it should be possible to make a set of statements like, “Heating 50 ml of 20 °C tap water in a 100W microwave for 90 seconds is 90% likely to reduce the time required to freeze it in a 1 m³ freezer by 35%.”

Why the citizen-science approach? I suspect that rather than trying to control all the known factors to produce the desired result, we instead want to track as many factors as possible to characterize the space of results. This particular effect will probably require a “vast multidimensional array of experiments“* to characterize properly, so enlisting a large number of citizen scientists makes a lot of sense.

Besides, each and every one of the test participants can have fun guessing at the real causes involved. Who doesn’t love a little armchair theorizing?

* Yes, I’m ‘citing’ Wikipedia. The original article cited there is inaccessible, and the rest of the Wikipedia summary is informative stuff.

this is not a science blog post

I (and Global Spin) have changed a bit over the last few months. Nothing you’d notice much, but I’ve set aside a few projects and picked up a few others. Specifically, I’m starting the long road toward becoming a licensed scientician.

Long story short: Global Spin is shifting towards science blogging. For the remainder of 2011 I’m going to post something sciencey once a week, probably on Tuesdays.

Older posts will still all be here; in fact, I’ve fixed the archives list in the sidebar so it shows posts going back to 2003. However, the focus going forward will be on science, culture, space, and technology. Those four categories catch most of what I’ve posted in the last two years anyway, so it won’t be a big shock.

I’ve also streamlined the site a bit. It’s not a community place anymore; social-media sites are much better at that now. It’s not even a place to store my personal commentary on the rest of the web; Tumblr and Twitter and Reader (oh my!) fit that need nicely.

One thing I’m going to try (and maybe go back on): I’ve turned off comments on these posts. Again, most of the commentary seems to happen elsewhere, so having those empty boxes at the bottom of each post seems a bit archaic. If you disagree, contact me and I’ll reconsider.

The motto hasn’t changed, though: We still protect our freaks.

To Science!