The Inclined Plane on Wikipedia

For those who live under a giant rock: Wikipedia is a user-created web-based encyclopedia. In conversation, I usually refer to it as a compendium of “common knowledge,” realizing of course that many elements of common knowledge are not common, and that many elements are flat wrong. Case in point: the Wikipedia entry on the inclined plane. (I refer to the article as it appeared on Sunday afternoon, 28 October 2007. The section on which I comment is reproduced in its entirety below, including the figure and text.)

The inclined plane is treated in detail in virtually every first-year physics course on the planet. I suspect that nearly everyone who took physics in college remembers it. We use it to teach students the quantitative aspects of Newton’s second law in two-dimensions, and to introduce friction. The Wikipedia article, although somewhat brief, touches on both of these. If I were grading the entry as an answer to a exam question, it would earn 3 out of 5 points, meaning that it gets some things correct, but that it also reveals major errors of fact or reasoning unacceptable for a first-year physics student.

Five-Sentence Movie Reviews (vol. 2)

It’s Friday, so if you have nothing to do this weekend but watch the Red Sox screw up the universal yin-yang even more by actually winning another World Series, allow me to recommend three great movies for your viewing pleasure: Spirited Away (2001), Night of the Demon (1957), and 12 Monkeys (1995).

Atheist Arguments

At Maverick Philosopher, William F. Vallicella has written a brief but insightful post about common atheist objections to theistic belief. (Hat tip to Brian Trapp for finding this.) I’ve considered wading into these waters myself, but my first blog taught me the importance of sticking primarily to subjects I understand well, such as physics, astronomy, bicycling, and watching movies and technophonic beer commercials. I dabble in theology or apologetics at my peril. But over the years I’ve encountered enough thoughtful, reasonable atheists to identify four broad types of objection to religious faith:

Blogroll Addition: Hobo Stripper

I don’t normally make any kind of announcement when I add a new blog to my blogroll. That listing is really more for me than my readers, since it provides a convenient way to bookmark the blogs I read most often. A quick survey of my blogroll reveals that nearly all the blogs are focused on either theology or science. But recently I wandered onto a blog that I have found endlessly fascinating: Hobo Stripper.

Coulomb’s Law and the Direction of the Force

Coulomb’s law presents a unique challenge to physics students struggling to understand how magnitude and direction can coexist in the same quantity–a vector. The difficulty with Coulomb’s law is that electric charge, a property of certain subatomic particles, comes in two types, arbitrarily called positive and negative. For example, the electron carries a negative electric charge, and the proton a positive electric charge. (They have the same magnitude, or amount, of charge.) Because charge can be positive or negative, Coulomb’s law often produces answers that are easily misinterpreted with regard to the direction of the force.

Five-Sentence Movie Reviews (special edition)

My five-sentence movie reviews are normally reserved for DVD titles, since I don’t get to the theater too often. But today, I give you The Kingdom.

The Kingdom (2007)
“This is a very bad neighborhood.”

Lollipops and marbles figure in this action-packed version of “CSI” goes to the Middle East. After putting all its creative energy into the opening credits, The Kingdom offers 90+ minutes of Hollywood shoot-’em-up cliches: the good guys are indestructible expert marksmen, never run out of bullets, ever, and never get shot, until it’s time to make the audience cry. One character suffers a horrible ordeal that would send any ordinary human being into several years of psychiatric care, but through the magic of the movies he recovers with nary a mental scratch. Indeed, this same individual seems to exist only to twice ask an invasive and insensitive question, the second time so as to set up the final 30-second sequence in which The Kingdom makes its Big Point. It’s well taken, but after watching this film phone in its morality with two or three montages of dreamy music and sad eyes, all I could think of was, hey, this is where the remake of Night of the Living Dead (1990) ended up. But The Kingdom is well-executed on a technical level, so I enjoyed not liking it.

A Nice Bike Ride Up Pilot Mountain

Pilot Mountain is located in Surry County, North Carolina, between Mount Airy and Winston-Salem on highway 52. Near the top of the mountain is a popular state park with picnic tables, several hiking trails, and breathtaking views of the region south of the mountain. The climb to the top is a wicked 2.5-mile stretch of 10% to 15% grade, with several switchbacks through the middle, steepest section. It’s unrelenting. There are no level parts where you can stop and get going again without risking death while trying to clip in. A climb like this takes away the anesthesia of your basic 30-mile Saturday ride. It hurts, a lot; and it drains away whatever you bring with you.

Fun With Orbits, Or How to Slow Down by Speeding Up

Orbits are cool. Let’s see how, shall we?

When a satellite orbits the Earth in a perfect circle, it experiences a centripetal acceleration that depends on its orbital speed v (a constant) and its orbital radius r (also constant):

A centripetal acceleration changes only your direction of motion.  A tangential acceleration changes your speed.  In your car, your steering wheel produces a centripetal acceleration, and your gas and brake pedals produce a tangential acceleration.

The centripetal acceleration experienced by an orbiting satellite is due to the Earth’s gravitational field:

where G is the universal gravitational constant and M is the mass of the Earth. (If you’re going to build a universe, you must decide how strong the force of gravity will be. You do this by setting the value of G. In our universe, and perhaps others, G has the value 6.673 x 10^-11 in SI units.)

Five-Sentence Movie Reviews (vol. 1)

This is the first post in the series. You have no time to waste, so I’m getting right to the point with these puppies. Every now and then, I’ll throw in a sixth sentence at no charge.

Dark Star (1974).
“Don’t give me any of that intelligent life crap, just give me something I can blow up.”

John Carpenter’s directorial debut began as a student film in the early 70s. The producers demanded new scenes, but the DVD has Carpenter’s cut. Weary space travelers, twenty years out from Earth, contend with boredom, a lack of toilet paper, an alien beach ball, asteroid storms, and an artificially-intelligent bomb that has decided to detonate before leaving the ship. One of the astronauts (Doolittle) engages the bomb in a hilarious philosophical debate about its own existence. If you’re in the right frame of mind, Dark Star is a gem; otherwise, it’s just an oddity from a director known to occasionally lose his audience.

Recreational Cycling Lessons (updated!)

First, some background. I’ve been biking for four years, but the first three of those were on a hybrid bike, a kind of cross between a mountain bike and road bike. I put about 3,500 miles on my hybrid in Alabama, a good portion of that compiled from my daily commute to work during 2005-2006. The hybrid followed me to Virginia in the summer of 2006, and the open country roads convinced me it was time to upgrade to a road bike. So January 2 this year, I spent all the money I had on a cheapest floor model at the Greensboro Performance store. I’ve been in love with my bike since I rolled it out the door.