Data Acquisition and Analysis for Children
The Measure activity on the XO accepts electrical signals through the sound port, and displays them on the screen. This makes the XO into a digital oscilloscope. The signal can be displayed in time domain, graphing signal strength against time, or in frequency domain, with a sequence of signals subjected to the Discrete Fourier Transform to break it into different frequency components. By applying signal processing, analysis and statistical algorithms to signals in either domain we get a powerful tool for scientific or engineering inquiry.
Any available physical effect can be used to generate a controlled electrical voltage, allowing it to be measured through the sound port. There are also numerous measuring devices with USB interfaces. We can analyze data from them in the same way.
We can also put control signals out based on measurements made. With these signals we can control experiments, or create systems to control devices of many kinds: for example heating, cooling, lighting, irrigation, patient care...
The camera in the XO can capture digital images and videos, including time-lapse video. Two-dimensional image processing and analysis and three dimensional video analysis are also powerful tools.
What, then, should children inquire into? Why, everything within reach, of course. They should be the William Gilberts, Luigi Galvanis, Alessandro Voltas, Ben Franklins, Count Rumfords, Humphrey Davies, Christian Ørsteds, Wilhelm Röntgens, Anders Jonas Ångströms, Thomas Edisons, Nikola Teslas, Marie Curies, George Washington Carvers, Buckminster Fullers, Francis Cricks, and James Watsons of their nations and peoples.
 Acquiring data
 Sound port
 Sensor Products
 Building Sensors
 Measure activity
 Air and Water Quality
 Health and Telemedicine
 Frequency Analysis
 Statistical Analysis
Yoshiki Ohshima to bens, OLPC
Ben and everybody,
The multiple-click problem prevented me from trying the acoustic distance measurement activity for a while, but finally I could do it last night on 637. This is pretty cool!
This reminds me of a story I heard from my boss and I thought you would be interested in it, too:
The graph activity was by some Physics professors at Tufts University, including Ron Thornton (who has been a major figure in physics education via computers since the Apple II). He has lots of stuff online (but I couldn't find the specific reference for this work (ca. 1990).
Basically, they found that a pre-test that would accurately predict the final grade was aptitude at reading graphs. Then they decided to try teaching some of their students how to read graphs -- and one of the main ways was to use a Polaroid camera range finder on the screen of the computer and the student using whole body movement back and forth to try to match different graphs on the screen: distance, velocity, acceleration, etc. They reported that this worked very well. We made a Hypercard version of this and tried it on children and teachers and found it worked very well.
Basically, looking at a graph and acting as a component or derivative of the graph is a great way to improve physics "sense" and it results in a better grade. He thinks that using the "whole body" instead of just finger tips is a key. This would be a great match with Acoustic Measure.
For this purpose, perhaps the interval of noise should be configurable and can be made shorter, and the read-out values should be able to be used by other things like a graph drawing/showing program.
Also, have you thought about making an explanation for kids, perhaps in the form of an "active essay"? The current implementation is a bit like a magic, and I bet many kids who try it would say: "it can measure the distance because they are 'talking' to each other" or something like that based on the "story mode" of thinking when asked how it works. A kid-accessible scientific explanation would be very nice. Since the essence of the measurement should be very, very small (perhaps just one or lines, leaving all the details of binary sequence and speed of sound variation), that would be a quite fun reading for kids.
Just my 2 yen.