June 9, 2009
Ethan at Starts With a Bang busts two Galileo myths.
1) That Galileo actually dropped weights off the Leaning Tower of Pisa. He almost certainly didn't. Like the story of George Washington and the cherry tree, it's an instructive parable not at variance with the character of the man - but not an…
June 8, 2009
Just 24 light-hours away it's still Sunday, right? Oh well. On to the math!
If you ask a mathematician to define a circle, you'll probably hear something along the lines of "A circle is the set of points in a plane equidistant from a given center point. The name of the distance from the center…
June 6, 2009
Our landings have failed and I have withdrawn the troops. My decision to attack at this time and place was based on the best information available. The troops, the air and the Navy did all that bravery could do. If any blame or fault attaches to the attempt it is mine alone.
- Gen. Dwight…
June 5, 2009
I don't know if you've been reading Photo Synthesis, but if you haven't you're missing a real treat. Currently there's some incredible photography and video of amateur rocketry at fairly large scales. Amazing stuff. A hundred years ago the idea that an amateur of comparatively middle-class means…
June 4, 2009
Reader Abby Normal(!) writes in with an excellent question:
Something in your post about Physics in Star Trek, May 18, 2009, has been bouncing around my brain. You stated that a black hole has the same mass, and therefore gravitational pull, as it's parent body. That makes perfect sense. But as I…
June 3, 2009
There's many, many sports out in the world that involve sharply hitting a ball with something. Baseball, tennis, golf, cricket, polo, you name it. After being hit, a ball describes a trajectory determined by the gravity of the earth and the interaction of the ball with the atmosphere. This can…
June 2, 2009
All right ladies and gentlemen, today we're performing an experiment! More of a demonstration, really, but one that's very easy and will impress your friends. You will need:
1) One remote control.
2) One camera phone.
The vast majority of remote controls operate via an infrared light-emitting…
June 1, 2009
This is the conclusion of the Ritz variation discussion we've been doing. Tomorrow we'll get back to less arcane and more entertaining physics, I promise! We're capping things off today by demonstrating the actual technique in detail for an example where we already know the answer. What we're…
May 31, 2009
Nobody ever asks the interesting questions at presidential press conferences. But if somehow I could choose a question, it would be this:
"Mr. President, has the NSA solved the integer factorization problem?"
Of course it's unlikely he'd know off the top of his head, and even if he did he…
May 30, 2009
There's a lot of important things going on in the world. Kim Jong Il is exploding nukes and launching missiles over Japan. A Supreme Court justice has been nominated. The treasury bond market experienced its steepest yield curve ever.
Whatever. Today we talk about Jon & Kate Plus 8.
Jon and…
May 29, 2009
A few days ago we had an interesting discussion about the actual nature of light waves with respect to the informal qualitative presentation of light waves found in intro textbooks. Because I have the best set of physics blog readers in the world, a fascinating discussion ensued with CC and Neil…
May 28, 2009
Continuing from yesterday's post on approximation methods in quantum mechanics, here's another common method worth a close look. It's one of my favorites, because it's a rare technique in which you can just make something completely up from thin air and it will very probably work well nonetheless…
May 27, 2009
We haven't done an actual straight-up physics problem in a while, much less one above the level of undergraduate freshman physics. There's a reason: it's roughly as niche as it's possible for an internet post to be. But on the other hand, surely someone ought to do it every once in a while. So…
May 26, 2009
It's 10pm on a Sunday night, and I'm driving west on Interstate 10 right through the middle of downtown Houston. Focused on getting to my destination safely, I obey the traffic laws and proceed through the comparatively deserted interstate at the maximum speed allowed by law. To experimentally do…
May 25, 2009
It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived.
- George S. Patton, June 7, 1945.
On this Memorial Day, we remember those members of the armed forces of the United States who have given their lives in the service of this, our Republic. We are…
May 24, 2009
Pick a two-digit number. Anything from 0 to 99 inclusive will work, because the single digit numbers can be considered to have a leading zero. Add the digits together. Subtract that from the original number. So if you started with 12, you add the digits to get 3, and subtract that from 12 to…
May 23, 2009
Yesterday we talked about how fermions and bosons had different values of spin and thus their wavefunctions had different symmetry properties. In particular, fermions are antisymmetric under exchange of particles. We'd like to write the overall two-particle wavefunction in terms of the individual…
May 22, 2009
Last time on Sunday Function we talked about two types of symmetries that a real function might have: odd and even symmetry under reflection about the y-axis. Much more than I expected even as an undergraduate student, these types of symmetries turn out to be of amazingly fundamental importance in…
May 21, 2009
Transverse or longitudinal waves, purely as a matter of aesthetic preference? Transverse all the way, of course.
Not that there's a huge difference mathematically speaking. It's more of a species-type categorization than a rigorously formal one. Transverse waves oscillate perpendicular to their…
May 19, 2009
In some ways, a crowd at a stadium has two possible overall states. They can be a normal crowd, or they can do the wave. But first, some background:
A gas isn't usually too hard to model at the statistical level. Treat is as a large collection of free particles and you're pretty much set. For…
May 18, 2009
I've never been much of a Star Trek fan. But given the subculture of nerdery in which I've been proud to spend much of my life, I've managed to pick up a fairly tremendous amount of the lore by osmosis. I've seen a pretty good percentage of the original series as well as the two good films (II…
May 17, 2009
I'm out of town, visiting family and friends in the period between the end of the summer and the time things get cranking back up later this summer. One thing I did do on Friday was catch the new Star Trek. I'll save the review and "physics of" posts for later this week. I'll be honest and admit…
May 14, 2009
Somewhat apropos of yesterday's entry in the perennial "what's science?" discussion comes this graph from Innocent Bystanders. The graph is originally from a report put out in January by the government's Council of Economic Advisers and the (then) Office of the Vice President-Elect, projecting the…
May 13, 2009
If you're reading this the morning it's published, there's a good chance that right at this very second I am sitting with pen in hand doing battle with a statistical mechanics final. Topics: fermions at zero and low temperature, virial expansion of the equation of state, critical constants and…
May 11, 2009
The little picture of me in the left sidebar was taken on the northeast shore of Arkansas' Lake Ouachita two summers ago. It's a beautiful place where you can experience nature in a peaceful and quiet way.
There were several of us who went, and one of them gave me a book of his that he'd finished…
May 10, 2009
Let's do two functions today. As sometimes happens, in this case we're not so interested in the functions themselves as the fact that these functions happen to be part of a general class of functions. Just as we can classify the real numbers as even, odd, or neither (numbers like pi, 1/2, and the…
May 9, 2009
You know what I've been delinquent in? Posting about some of the other blogs out there that I take for granted as being great, because they are. A random sampling of good stuff:
Swans on Tea discussing entanglement in the popular press.
Chad Orzel on the physics of Rumpelstiltskin.
Dirac Sea on…
May 9, 2009
A while back, Texas governor Rick Perry made the news for the following comment:
We got a great Union. There's absolutely no reason to dissolve it, but if Washington continues to thumb their nose at the American people, you know, who knows what may come out of that.
All things considered it's a…
May 8, 2009
Three question E&M I final today, roughly as follows.
1a. As a starting point, calculate the electric potential on the axis of a ring (radius a) of uniform charge. (trivial)
1b. Use the expansion in Legendre polynomials to do an off-axis extrapolation of 1a to find the potential everywhere. (…
May 7, 2009
Ryan North of the exceptionally brilliant and somewhat esoteric Dinosaur Comics penned a comic a while back about the possibility of being the perfect detective by using physics. Quoth T-Rex in the strip:
Someone in the room says something to another person, and then they both leave. Assuming you…
