August 21, 2009
In the last post I made an offhand mention of wave dispersion, which is the phenomena of different wavelengths propagating a different speed. In general this does exactly what it sounds like it should. It disperses the light. If you start off with a tightly grouped bunch of runners, the pack…
August 19, 2009
All right, the answer to yesterday's question about the maximum speed of a stadium wave, as many commenters rightly said, is "as fast as you want." The comments went into some depth on this, and I like the way Zifnab put it:
I mean, if you've got two independent agents doing their thing, the "…
August 17, 2009
The wave. We've talked about it before. It's where people in a stadium stand up and sit down in sequence so that a wave of standing people travels around the circumference of the stands.
They have a typical speed of around 12 m/s, though it is by no means entirely universal. You could certainly…
August 17, 2009
Let's say there's an interesting but somewhat obscure book I'm interested in. Say, Electromagnetic Pulse Propagation in Causal Dielectrics. It's a very technical work about a very specific subject, so the total print run was probably very small. Maybe a few hundred or a thousand or so? I have…
August 16, 2009
There's an interesting book I'm working on called The Fall of Rome: And the End of Civilization, by historian Brian Ward-Perkins. He argues (against a prominent modern school of thought) that Rome did indeed fall rather than merely change, and that European civilization really was wrecked pretty…
August 15, 2009
Today I bought a sandwich at Subway. 12" ham on "Italian herbs and cheese" bread, American cheese, lettuce, tomatoes, bell peppers, sweet onion sauce. After tax, the cost was $5.41. I handed a $10 bill to the young guy behind the register. By young I'm guessing 18ish.
As such I was going to get…
August 14, 2009
And God said, Let there be light: and there was light.
- Genesis 1:3
This post is going to need the standard math disclaimer. Though there's math that looks horrible, you don't actually have to know any math to follow the ideas. Give it a try!
Over this week we've looked at the four Maxwell…
August 13, 2009
Fundamentally Maxwell's equations describe the origins of electric and magnetic fields. Given a set of conditions on the right hand side of the equations, you'll have fields described by the left hand side. Between the four equations the fields are uniquely specified, and there is nothing more to…
August 12, 2009
So far we've seen that electric charges create electric fields. We've also seen that magnetic charges would create magnetic fields if there were any such things, but there aren't. If you're in the business of creating electric fields, as the entire electric power industry is, one way of doing so…
August 11, 2009
In our examination of the first of Maxwell's four equations, we saw that magnetic charge doesn't exist as far as we can tell. On the other hand, electric charge permeates every aspect of our existence. The motion of charged electrons is one of the central pillars of modern civilization. The way…
August 10, 2009
All this week we're going to be briefly looking at James Clerk Maxwell's greatest contribution to physics - his theory of electromagnetism. The consequences and applications of the theory fill many volumes, but the conceptual and mathematical foundations of the theory can be expressed as four…
August 9, 2009
All right ladies and gentlemen, take out your calculators. Punch in the number 4. Whack the square root button. What do you get?
Unless I am badly mistaken, you're going to get the number 2. As you probably remember, the square of a number is just that number multiplied by itself: 3 squared…
August 7, 2009
The excellent readers of this blog have left numerous astute comments about the Nuke the Moon post, assessing the difficulty of knocking aside asteroids via nuclear explosions. The two most common themes are orbital mechanics and using the lunar mass itself in a sort of mass-driver configuration…
August 6, 2009
Graduate school is like the previous 16 years of school in that you learn things and take classes, at least for the first couple of years. On the other hand it's also much more like a regular job than the previous schooling. You do work that's unrelated to class, and you get paid. Maybe not a…
August 5, 2009
Reader Scott writes in with a question:
Okay, let's assume something knocked the moon out of its orbit and it is going to crash into the earth in an arbitrary amount of time. (7 days?)
You are humanity's last hope. You have the entire nuclear salvos of the USA and Russia at your disposal, which are…
August 4, 2009
P.Z. Myers is not happy about Obama's selection of Francis Collins to head the National Institutes of Health. Why? Well, as you probably know, Myers is an outspoken atheist and Collins is an outspoken Christian. Myers is happy to point out that his opposition is not due to Collins' beliefs per…
August 4, 2009
A few days ago we calculated the radiative power output of a very radioactive source like cobalt-60. CCPhysicist suggests we also calculate its surface temperature. Sounds like a plan!
A radioactive plutonium pellet, glowing red hot. Still much less radioactive than our hypothetical cobalt.
It…
August 3, 2009
You know what's gonna happen? I'll tell you what's gonna happen. Troops are now forming behind the line of trees. When they come out, they'll be under enemy long-range artillery fire. Solid shot. Percussion. Every gun they have. Troops will come out under fire with more than a mile to walk. And…
July 31, 2009
I'm a bibliophile. I read books at an inordinate rate and have a tendency to buy them at an even faster rate. Here at Texas A&M I'm fortunate to have access to a library of more than four million volumes, a fantastic interlibrary loan service, and a breathtaking special collections library…
July 30, 2009
As a student I know that toward the end of the semester it's sometimes a struggle to pay attention and retain motivation. As a teacher I have to try to fight that tendency in whatever way I can. It's not necessarily possible to make a physics quiz entertaining, but sometimes they can at least be…
July 28, 2009
We're not too far from the end of the Physics 202 class I'm helping teach, and as we finish things out we're learning about the particle nature of light and the wave nature of matter. It's really the very basics of quantum mechanics. One of the applications of this kind of knowledge is the…
July 27, 2009
This weekend I was at the movies with my lovely significant other watching The Proposal (verdict: about what you'd expect). Unusually for a by-the-numbers romcom, the pre-film previews showed no fewer than two promising science fiction films.
Science fiction is difficult to cleanly describe - it's…
July 26, 2009
We've done a lot of discussion of the concept of integrals of a function here on this blog. Their definitions and applications are so broad as to defy any one-sentence description, but one of the most basic is the idea of the area under a curve. More precisely it's the signed area under the curve…
July 25, 2009
Roughly a week or so ago the ScienceBlogs front page was discussing the new online videos of the Feynman lectures. Somehow they found one of my old posts on the subject.
What I haven't really seen pointed out that the new online video isn't actually "the" Feynman Lectures. "The" lectures were…
July 24, 2009
Far be it from a ScienceBlog to bloviate insufferably about current events, but I suppose I should weigh in on the whole Henry Louis Gates thing. I suppose this because I've had a very similar thing once happen to me. First Gates' story, then mine.
The accounts of Gates and the arresting officer…
July 23, 2009
Here's a neat little news article about humans glowing in the dark.
The human body literally glows, emitting a visible light in extremely small quantities at levels that rise and fall with the day, scientists now reveal.
Past research has shown that the body emits visible light, 1,000 times less…
July 22, 2009
This week the science blogosphere has been spending a lot of time on space exploration and the science of understanding the universe outside our own planet. At risk of being the buzzkill distracting from all the cool space travel history and heated debates about NASA's future, I think it will be…
July 21, 2009
There's been some discussion around the web of Jupiter apparently getting walloped by something, probably a comet. As with the more famous Shoemaker-Levy 9 impact, the result is a small dark blot in the clouds of the Jovian upper atmosphere. Small is a relative term - small spots on the surface…
July 20, 2009
Forty years ago two human beings traveled a quarter million miles in a tiny metal capsule and stepped out onto the surface of the Moon. It was the most dramatic footfall in the history of our species, I am in absolute awe of all the Apollo program accomplished. Though it's a long shot, I'm…
July 17, 2009
At the time I write this sentence it's 10:13 pm. The sun has been under the horizon for almost two hours. It's 93 degrees Fahrenheit outside here in College Station. I believe it peaked out right at 100 during the day, and it feels hotter in the sun. Even the animals are clearly not pleased.…
