Tapdancing Goats » Physics

Double Pendulum Simulation

Alex — Thu, 18 Aug 2011 07:53:27 +0000

I’ve been playing around with some of the new features in HTML5, particularly to see how the canvas stacks up to Flash. One of the things I wanted to test was javascript performance, so I ported this Flash toy I wrote a few years ago. It’s a physical simulation of a double pendulum system. It’s interactive, and it can export the line drawing it produces as a PNG.

How did canvas+JS do? The export was a lot easier: I had to write a PNG encoder in Actionscript for the original version! Pretty much everything else was harder. Canvas has features similar to Flash 5, and I missed modern Flash’s rich standard library. CSS layout is still somewhat inferior to Flex for GUI design, as the layout options are less flexible.

One of the appeals of canvas is mobile support, but I was disappointed by the performance on my Motorola Droid. Just clearing the background on a canvas larger than 500×200 took the frame rate to single digits, and I couldn’t find a reliable way to make the canvas fill the screen if other elements were present (I didn’t look too hard, since a canvas that large was unusable). The javascript performance was fine, it was just the drawing that caused problems. Let me know if you get better results on different hardware, I’d love to know that this can work better.

Overall, canvas shows promise, but I don’t think it’s ready to replace Flash for complex graphical applications.

Spin: The Game

Alex — Fri, 11 Mar 2011 07:12:23 +0000

Spin is a new Flash game I’ve been noodling on for a little while. It’s a Puzzle Bobble type game, except that the balls can freely spin like a pinwheel. The rotation is physically accurate, so as balls fall off of the board it changes speed and direction. When a ball hits the board the ball’s momentum is transferred to it, so if the board is turning slowly you can speed it up or make it turn the other way by firing the balls at it.

The feature list was miles long, but I’m getting too busy to work on it. Look forward to a second version when I can get back to it.

There Is So Much Here To Discover

Alex — Sat, 24 Apr 2010 02:36:53 +0000

The alt text in today’s XKCD is a beautiful little poem.

Telescopes and bathyscapes
and sonar probes of Scottish lakes,
Tacoma Narrows bridge collapse
explained with abstract phase-space maps,
some x-ray slides, a music score,
Minard’s Napoleonic war:
the most exciting new frontier
is charting what’s already here.

I formatted the lines, so it might not scan the way Randall wanted. Tough.

Easy Scientific Notation In LaTeX

Alex — Fri, 02 Mar 2007 21:46:30 +0000

I use LaTeX for all my physics homework and lab reports, and I’ll be using it for a master’s thesis in the next few years, so I’m constantly adding to my library of LaTeX commands to save some typing. Here’s a good one when you need to use scientific or engineering notation. Put the following in the document preamble (before \begin{document}):

\providecommand{\e}[1]{\ensuremath{\times 10^{#1}}}

Then, typing

The [111] crystal planes are 3.2\e{-10} m apart.

gives you: The [111] crystal planes are 3.2×10^-10 m apart. whether or not you’re already in a math environment. If the exponent is just one number, you can omit the braces, like this: 3\e8 m/s. Cool, huh?

(Of course, for 10^-10 m you can just use Angstroms, \AA. If you’re in a math environment, use \text{\AA}, or else the circle won’t line up with the A. That is, if you’re okay with non-SI units.)

Bold vectors in LaTeX

Alex — Tue, 13 Feb 2007 02:26:53 +0000

Vectors can be typeset in LaTeX with the command \vec, which decorates the argument with a little arrow. This was cute at first, but it doesn’t look very good, especially in fractions. Textbooks use bold face for vectors, so here’s how to do that in LaTeX.

\let\oldhat\hat
\renewcommand{\vec}[1]{\mathbf{#1}}
\renewcommand{\hat}[1]{\oldhat{\mathbf{#1}}}

This also makes unit vectors (typeset with \hat) bold.