Discovering the Discworld: Where to Start With Terry Pratchett

Rowan Kaiser asserts that Mort‘s the best place to start to discover the wonderful novels of Terry Pratchett.

the Discworld books combine silliness, satire, philosophy, and strong characterization to create a unique, often wonderful tone that’s more than capable of supporting a series with so many installments. But the number of installments can seem overwhelming, especially given that while the books have standalone narratives, they also have consistent sets of characters who develop over the course of the series, leading to an apparently complicated web of a few different, occasionally overlapping series-within-a-series.

–Kaiser (2011): Gateways To Geekery: Terry Pratchett novels in The Onion’s A.V. Club.

My recommendation would be one of her runner-up gateways — either Guards! Guards! or Wyrd Sisters — but she makes good points. Her third runner-up, Small Gods, which is one of the stand-alone novels is one of my favorites, and was my first Pratchett book. And it got me hooked.

Pratchett’s work is intelligent fantasy, in that it’s a lot like the hard science fiction I prefer. It sets up the rules of its universe and then follows them to their logical conclusions, no matter how absurd.

I often wonder how these books would appeal to adolescents since there’s a distinct possibility that much of the quite enjoyable satire would pass over their heads. The Amazing Maurice and his Educated Rodents won the Carnegie Medal for children/young adults, but while it retains Pratchett’s characteristic style and humor, it was written for a younger demographic, unlike most of his other books. I did get one student to read Small Gods, and her response, with a grimace was, “It made me think“.

Beating the Odds: The Sheer Improbability of Being Here

visual.ly posts and hosts some excellent graphics. The one below, calculates the nearly infinitesimal probability of just being born. There’s hardly a better argument for appreciating life.

It’s also a good example of working with probabilities [and] exponents. Very large exponents.

by visually via

Making a Non-Stick Frying Pan the Old Fashioned Way: Creating Polymers at Home

Cast-Iron-Pan — "Seasoning" a cast iron frying pan creates a non-stick coating. (Image by Evan-Amos via Wikipedia).

Back in the day, if you wanted a non-stick cooking skillet, your best option was to do it yourself by seasoning a cast metal pan. Sheryl Canter has an excellent post describing the science behind the “seasoning” process. The key is to bake on a little bit of oil to create a strong cross-linked polymer surface. This is a nice tie into our discussion of polymers and polymerization in the middle school science class; although I’m not sure how many of my students have actually seen a cast iron pan, or even know what cast iron is.

polymer-0235 — Normal polymers are long molecules made up of smaller molecules linked together, much like a paperclip chain.

polymer-0233 — Cross-linked polymers are created when the long chained polymers are linked together by cross-links. It makes for a much sturdier molecule.

To season, you coat the pan with a thin layer of oil and bake it for a while (without anything in it). Baking releases free radicals from the metal that react with the oil to create a cross-linked polymer that’s really hard to break down or wear out, and prevent food from sticking to the pan. Different, cross linked polymers are used in car tires for their durability, but probably not for their lack of stickiness.

Apparently, linseed oil is the best seasoning agent, but it might be a bit hard to find.

Most non-stick, artificial surfaces, are also made of polymers of hydrocarbons, silicon oxides and other interesting chemicals.

polymer-0251 — Making a cross-linked polymer with borax and polyvinyl alcohol.

In the lab, you can make your own cross-linked polymer “slime” by adding a solution of borax (sodium tetraborate) to a solution of polyvinyl alcohol (1:1 ratio of concentrations) (Practical Chemistry, 2008).

The result is a satisfying goo.

polymer-0254 — Cross-linked polymer "slime".

Media Profanity and Aggression

This research shows that profanity is not harmless. Children exposed to profanity in the media think that such language is ‘normal,’ which may reduce their inhibitions about using profanity themselves. And children who use profanity are more likely to aggress against others.
–Brad Bushman (2011) in a Brigham Young University Press Release.

Exposure to profanity in videogames and on TV appears to affect how teens view and use profanity, and makes them more aggressive. These are the key results of a paper by Sarah Coyne (Coyne et al., 2011). The full article is available online, but is summarized here.

While the first part, at least, of this result might seem obvious — that seeing profanity desensitizes, familiarizes, and leads to increased use — it’s nice to have some scientific corroboration.

The more disturbing result, perhaps, is the link between profanity and aggression. It’s a moderate effect, but the link appears similar to the connection between war games and aggression.

Profanity is kind of like a stepping stone. You don’t go to a movie, hear a bad word, and then go shoot somebody. But when youth both hear and then try profanity out for themselves it can start a downward slide toward more aggressive behavior.
— Sarah Coyne (2011) in a Brigham Young University Press Release.

Sling: A VPython Model Demonstrating Centripetal Force and Conservation of Angular Momentum

sling-anim-500 — Animation captured from the sling.py Vpython model. The yellow arrow shows the centripetal force. The white arrow shows the velocity.

Sitting in a car that’s going around a sharp bend, its easy to feel like there’s a force pushing you against the side of the car. It’s called the centrifugal force, and while it’s real to you as you rotate with the car, if you look at things from the outside (from a frame of reference that’s not rotating) there’s really no force pushing you outward. The only force is the one keeping you in the car; the force of the side of the car on you. This is the centripetal force. Given all the potential for confusion, I created this little VPython model that mimics a sling.

Centripetal Force

In the model, you launch a ball and it goes off in a straight line. That’s inertia. An object will move in a straight line unless there’s some other force acting on it. When the ball hits the string, it catches and the string starts to pull on the ball, taking it away from its straight line trajectory. The force that pulls the ball away from its original straight path is the centripetal force.

centrifA — Image from Stern (2004): (23a) Frames of Reference: The Centrifugal Force

Conservation of Angular Momentum

The ball rotating on the sling has an angular momentum (L) that’s equal to the velocity (v) times its mass (m) times its radius (r) away from the center.

L = mvr , angular momentum

Now, angular momentum is conserved, which means that if you shorten the string, reducing the radius, something else must increase to compensate. Since the mass can’t change, the velocity has to, and the ball speeds up.

momentum-diag — The ball on the string with the shorter radius has the higher velocity (moves faster). It also has a higher centripetal force. The ball for shortening the radius is not shown in this figure.

I’ve put in a little ball at the end of the string that you can pull on to shorten the radius.

Tangential Velocity

Once the ball is attached to the string, the centripetal force will keep it moving in a circle. If you release the ball then it will fly off in a straight line in whatever direction it was going when you released it. With no forces acting on the ball, inertia says the ball will move in a straight line.

The ball, when released from the string, flies off in a tangent.

To better illustrate the ball’s motion off a tangent, I put in a target to aim for. It’s off the screen for the normal model view, but if you rotate the scene to look due north you’ll see it.

What’s Wrong with Traditional Education

Alison Gopnik points out the people first start to learn by exploration (the same way scientists do), and then learn to do things well by apprenticeship.

When we actually start to look at the fundamentals, it seems children learn by exploring—by experimenting, playing, drawing inferences …. that kind of exploratory learning isn’t just the purview of scientists but seems to be very, very basic. …The other kind of learning that we see, not so much in preschoolers but in school-age children, is what I call guided apprenticeship learning, where you’re not just exploring and finding out new things but learning to perform a skill particularly well.

— Alison Gopnik in Fillion (2011): In conversation: Alison Gopnik in MacLeans.

Kate Fillion’s great interview with Gopnik, a cognitive scientist, is worth the read.

The traditional way of thinking about learning at a university is: there’s somebody who’s a teacher, who actually has some amount of knowledge, and their job is figuring out a way of communicating that knowledge. That’s literally a medieval model; it comes from the days when there weren’t a lot of printed books around, so someone read the book and explained it to everybody else. That’s our model for what university education, and for that matter high school education, ought to be like. It’s not a model that anybody’s ever found any independent evidence for. [my emphasis]

— Alison Gopnik in Fillion (2011): In conversation: Alison Gopnik in MacLeans.

Update

EV, in the comments, recommends Allison Gopnik’s TED talk. It focuses on babies, but is a pretty good presentation.

(via The Dish)

Murmuration: A Flocking of Birds

Amazing footage of an enormous flock of birds in flight by Sophie Windsor Clive.

Murmuration from Sophie Windsor Clive on Vimeo.

Brandon Kelm explains a little of how it works, mostly using terms like “scale-free correlation” and “criticality”, which pretty much sums up that we don’t know a lot about the phenomena.

NetLogo has a nice little Java model showing an attempt at simulating flocking. They give a good description of how there model works.

(via The Dish)

How the Electoral College Works

The Trouble with the Electoral College

Centripetal Force

Conservation of Angular Momentum

Tangential Velocity

Update