College of Arts and Sciences from American University Explores the Physics of Music on National Mall

kcollins — Tue, 19 Oct 2010 15:00:00 +0000

The physics of music is a greater way to appreciate music. This booth sounds quite interesting. Thanks CAS for helping get the word out about the Expo and coming to have a booth. Find the full post here.

By Kaitie O'Hare
October 13, 2010

Physics Professor Nate Harshman and High School Noura Jaber will demonstrate Chladni plates at the Expo.

Professor Harshman and High School student Noura Jaber experiment with Chlandi plates.

The physics department and audio technology programs are teaming up on October 23-24 to present "The Physics of Music" exhibit on the National Mall, part of the larger two-week long USA Science and Engineering Festival Expo taking place around the D.C. area.

"The Physics of Music" will be one of over 1,500 hands-on activities offered by over 500 of the nation's leading science organizations. "It's a who's who of science in the United States," says Physics Associate Professor Nate Harshman. "AU should have a bigger presence in D.C., and AU science should have a bigger presence in D.C. as well."

Harshman has been organizing this exhibit since February, collaborating with the audio technology program to create multiple hands-on demonstrations.

"I thought music would have an appeal that some things that were science, just for science's sake, wouldn't hit," says Harshman. "I like the idea of physics and music because it's supposed to be stuff for pre-teens and teens."

The exhibit, sponsored by the College of Arts and Science, features three demonstration tables, each showcasing a different aspect of physics and corresponding instruments or devices.

Harshman's arranged three tables exploring everything from acoustic instruments, such as the autoharp, Chinese singing bowls, Chladni plates, and Helmholtz resonators, to electronics demonstrations of a microphone and a theramin. This musical instrument detects the position of the players' hands with an antenna so that it can be played without being touched. Another table demonstrates auto tuning, a voice Fourier analyzer, and a Wii created by audio technology Assistant Professor William Brent that has been programmed to sing by adjusting the tone, volume, and vowel with the remote's motion.

Harshman hopes the exhibit will give young adults a better understanding of the physics behind music, and help them distinguish between analog electronic and digital electronic instruments. "People don't often realize there's a difference between the two, but there is," he says. But more importantly, he just wants kids to have fun.

The USA Science and Engineering Festival Expo runs from 10 a.m.-5:30 p.m. on Saturday, October 23 and Sunday, October 24 on the National Mall. For more information, please visit the USA Science Festival Web site.

kcollins Tue, 10/19/2010 - 11:00

Maxima can be useful

rallain — Tue, 13 Jul 2010 09:17:24 +0000

Maxima can be useful

The other day I found myself faced with six equations that needed to be solved algebraically. Just so you know, I am a big fan of paper for most of these cases - but this was out of control. I was making silly mistakes and causing all sorts of problems. What to do? My first though was to use some symbolic plugins for python. I tried sympy and it is nice. However, it was not giving correct solutions for solving 3 equations - I don't know if this is a bug or what.

Maxima

I think I found Maxima through Wikipedia's Computer algebra system page. It's free and free and runs on Mac OS X and Windows.

The point of this post is not just to tell you about this software, really it is to tell me about it. I probably won't use this for a while, and so I will forget what I did. First, some useful resources:

Introduction to Maxima. This intro by Richard Rand is very thorough. Basically, it has everything you need.
How to export your equation in LaTeX. This is something I found that seemed quite useful.

So, if you want to get a good start, look at the intro link above. But I will summarize a couple of quick things. First, entering expressions. One thing I did not like about sympy was that expressions were entered as 2x + y = 0 instead of 2x = -y. In Maxima, just enter the equation. Here are some rules:

Use normal order of operations stuff
Don't forget * for multiplication. If you do 2x, you will get an error. 2*x is ok.
You can use variables that are longer than 1 character, but it can't start with a number - x2 is ok, but not the variable 2x.
When you enter a statement, you must end with a ";"
The output of every entry is labeled something like - %o19. This is nice because you can refer to this output in later entries.

An Example

Let me show a simple example. I will use two of the kinematic equations to create a third kinematic equations - algebraically. Let me start with:

Now, to enter these two equations into Maxima:

Notice that you use normal (non-python) format for entering expressions - by non-python I mean that the "^" means raised to the power instead of "**". The output is formatted in a way to look a little nicer.

Now, I want to solve the second equation for t:

Here, I referred to the original equation by its output line number (%o3 in this case where that is an "o", not a zero). Next, I just want to substitute this expression for t into the first equation.

The command in line %i6 may look weird. But this is saying take the equation %o2 (which is the first equation) and substitute t = ... (which is equation %o5). Now I want to take this equation and solve for v2 - so that it is in its usual form.

I don't know why it gave the expression twice. Update: As pointed out in the comments below, this is because there are two answers, a positive and a negative. End update If you just wanted 1 answer, you could type %o7[1]; - I don't know why Maxima's arrays don't use the normal use of [0] being the first element.

Finally, if you want to get this as v2^2:

That is good enough to get some useful stuff done. Also, hello to future me. I am probably going to find this post 3 months from now when I forget how to do something in Maxima.

rallain Tue, 07/13/2010 - 05:17