Jeff Duntemann's Contrapositive Diary Rotating Header Image

science

Odd Lots

Odd Lots

Odd Lots

Odd Lots

Kids as Parametric Oscillators

Back in June, when Carol and I were in Chicago, we took our nieces to the school playground across the big field behind my sister’s house. We pushed them on the swings, as usual, and I considered that both girls are tall and muscular for their ages. So I asked, “Katie, do you know how to pump?”

“What’s pump?”

“It’s pushing yourself on a swing so nobody else has to push you!”

She looked at me funny. She does that a lot; it’s part of the Uncle Jeff job description. So while pushing her I prepared to answer the obvious question: How do I do that, Uncle Jeff?

I stood there for a second before I realized that I had not pumped a swing for, well, decades. I wasn’t entirely sure I remembered how to do it. I gave Katie an extra big push and jumped onto the swing next to hers.

Shazam! The mind may forget…the body remembers! In thirty seconds I was going way high, and was devising my tutorial for the scarily bright little girl three feet to my left:

As you go forward, pull back on the chains and stretch your feet out. When you start to go back, stop pulling on the chains and pull your feet underneath you.

Wait a minute. Wait one damned minute! How does that work? I mean, I’m not pushing against the ground or anything else, and not hurling reaction mass. I realized that while the body remembered clearly how to pump a swing, the mind could not explain it.

I vaguely and anciently recalled reading something about a swing with a kid on it acting as a parametric oscillator, but the details were just gone. My guess at the time was a good one: When you pump a swing, you’re raising and lowering your center of mass a little by “bending” the pendulum, synchronized to the timing of the swing’s motion. That adds energy during the forward motion of the swing. There are explanations all over the Web, but the one I found by Dr. William Case at Grinnell College was the best, including several short video clips.

It’s an amazingly subtle business.

I’m kicking myself now for not thinking to try the obvious enhancement, which is pushing forward on the chains at the rear extreme of motion. Next time.

Katie didn’t quite get it but she gave it a good shot (heck, I was at least six before my cousin Diane taught me circa 1958) and with a little practice she’ll remember it well past her sixtieth birthday in 2066, and possibly even into the 22nd Century.

Some things are just timeless.

Odd Lots

  • I hit a milestone the other day: 40,000 words on Ten Gentle Opportunities, which is at least halfway there and maybe (if I’m willing to settle for a 75,000 word story) more than halfway.
  • One of my readers sent a link to a page describing how to install the Insight debugger under Linux Mint. As my ASM freak friends will recall, I no sooner described Insight in Assembly Language Step By Step, Third Edition than Debian pulled it out of their distribution. Supposedly this method will also work for newer versions of Ubuntu. I need to test the repository under both distros, and will report when I do.
  • There’s a new nova in Sagittarius. (Is that redundant?) Mag 7.8–which is easy to see with binoculars, if you can separate it from the stellar mosh pit in which it appeared. Thanks to Pete Albrecht for the link.
  • Michael Covington sent a Google Ngram for the words “whosever” and “whoever’s” indicating that “whosever” has been on the run for a couple of centuries. It became the minority player about 1920 and has been down in the mud since about 1960.
  • Ok, I agree: This is the most brilliant kitchen gadget since the salad spinner. Or before.
  • I used to do this a lot, though I haven’t done it since 1977: pull the guts out of a photocopier. This guy’s blog, by the way, is news to me but should be on every techie’s blogroll. (Thanks to Jack Smith K8ZOA for the link.)
  • Haven’t heard much about software radio recently. Ars Technica just had a nice overview piece on it. The hardware keeps getting better, but all the promised weirdness (including new types of pirate radio) hasn’t happened yet. My theory: Wi-Fi is just a better weirdness magnet.
  • Foxconn is releasing a fanless nano-PC toward the end of summer, and I like the looks of it, at least if it’s got something better than an Atom in it. Roughly 7.5″ X 5.25″ X 1.5″. No optical drive. 5-in-1 card reader on the front panel. Under $300.
  • Talk about nutty brilliance for film promotion: RC drones in the shape of superhero-style flying people to hype the film Chronicle, which is evidently about…flying people. (Thanks to Pete Albrecht for the link.)
  • To inflate a Buckyball, just use a laser.
  • This sweet merlot (scroll down) was lots better than I thought it would be, especially for a hot summer evening’s barbecue. May be hard to find outside Colorado. No least hint of concord grape, for you mutant-blueberry purists. About $15.
  • Yet another sign that we may be winning the Fat Wars: Fat-free dressing is bad for you.
  • Still yet another sign may be that the grocery store near our condo outside Chicago carries a sort of spreadable lard called “smalec.” This is the best-kept secret in the food world; it took me ten minutes to even find a picture of it. It was brought here by Polish immigrants and is no less healthy than butter, though I have no clue as to its taste.
  • As if we didn’t have enough to worry about, well, the latest home hazard is swallowing loose bristles from your grill brush. My brush is at least five years old and failing. Looking for another technique. (Again, thanks to Pete Albrecht for pointing it out.)
  • This sure sounds like a hoax, but there could be a zombie apocalypse theme park in Detroit’s future. The concept suggests that time’s about up for the zombie craze, so I’d better get my novel (which contains dancing zombies) shambling on to completion before the whole thing caves in.

Odd Lots

  • I’m behind on a great many things, especially fiction writing and replying to email, so bear with me until I get dug out from under the pile. Exchanging offices within a house is precisely the same as moving two offices, and that means a lot of boxes and a lot of bother, exploding intercoms being the least of it.
  • I didn’t expect this wine to be as good as it actually is. About $11.
  • The weather’s been beautiful here, so yesterday I was going to get out on the back deck with my Icom 736 and work the world. That was, of course, the day that sunspots basically vanished on the visible face of the Sun. What does it mean to have solar flares but no sunspots? Nobody knows.
  • Thanks to many people (Jim Strickland being the first) who wrote to tell me about a “smart sand” project at MIT that is the first step toward the sort of nanoreplicator I postulated in my Drumlins stories: Tap in a 256-bit code, and some “smart dust” (very smart) in a stone bowl assembles something for you. I love it when my crazy dreams come true!
  • Single-atom nanotransistors can now be reliably made, rather than hunted for. (Thanks to Roy harvey for the link.)
  • From Michael Covington comes a link to a fascinating article about the other kind of abduction: abductive logic. If you’re a Sherlock Holmes fan, don’t miss it!
  • The Colorado state law that led Amazon to nuke my Associates account has been declared unconstitional. No word from Amazon as to whether I can have my account back.
  • I would probably buy one of these if I could find one in stock somewhere.
  • Jack Tramiel has left us, having created quite a raft of famous computers, including the very best forgotten computer ever.
  • I checked the date on this one, but it was nine days too late to assume it’s a hoax. One might argue that solar panels are more elegant, but you can’t make buffalo spaghetti sauce in a solar panel.
  • I’ve seen more dumb YouTube posts than I’m willing to admit, but this one takes the cake for sheer willful stupidity. I knew how this worked in 1959, when I was 7.
  • Kids, this is futurism. All we need now are better tacos.

Odd Lots

Odd Lots

Odd Lots