You see in my experimental determination of the location of the accelerometer in an iPod, I used two different iPhone apps. Let me briefly mention some of the free iPhone apps that give you acceleration data.
AccelGraph: This is one of the apps I actually used. What do I like about it? Well, it can record x, y, and z acceleration data and then you can email it to yourself. What could make it better? How about a timed start to record (like start recording in t seconds) and a preset record time. This would allow you to set up your experiment and get your iPod set up before you start. As a bonus, it would be great if it gave you a sound countdown to starting the recording. As a triple bonus, it would be super-awesome if you get get live acceleration readouts on a computer near by.
AccelMeter: I wanted to use this app, I really did. I wanted to use it because it is cool. In short, this app shows an acceleration vector in 3-d. Pretty awesome. You can also "lock" the vector so it can only change in one direction at a time. My plan was to use VNC on a jailbroke (that sounds funny) iPod to record the screen of the iPod as a video. This failed. Still, it is a fun app to play with. Not very useful since it doesn't save any data.
Acceleration App: This is a pretty basic, but simple acceleration app. It gives the acceleration in all three directions and it stores the "maximum" value. You can not save or send the data.
Gravity Meter: Basically, this apps just attempts to give a value for the local gravitational field (which it calls the acceleration due to gravity). I have not played around with it too much - so I am not sure how accurate it is. It would be cool if you could do some of the things it says it could do: see changes due to altitude, see changes due to influence of the moon etc...
SparkVue by PASCO: I had high hopes for this app. It is supposed to be a way to collect data on your iPhone using PASCO's bluetooth sensors. Well, I don't have any of these sensors so I could not test that. It also can collect data with the built in accelerometer. However, in my short time playing with it, it seems you can only collect data on the total magnitude of the acceleration. Oh, but you can send the data to yourself. Maybe this app will get better in a future update.
I was wrong and it was my fault. Brian for PASCO emailed me to point out some of the features of the SparkVue software. It appears that you can indeed look at things other than just the resultant acceleration. You can also display the acceleration in units of "g's" or in m/s/s. See, if you just start using it and collecting data right away (as I did), you can't change these things. If you are just the tiniest bit patient, you learn a lot.
Actually, SparkVue has another feature that is really nice. Timed data collection. You can set the time that it runs before it stops. You can also save acceleration data at up to 50 Hz. It would be awesome if you could set a "trigger" for data collection. Maybe if the acceleration goes over some value, it starts recording.
Here is a screen capture from the part of SparkVue that allows you to change the collection settings (the part I missed before):
This post and your previous one are fantastic! I recently bought an iphone and have been wanting to do something with the accelerometer but I hadn't looked into how to use it or what data you can take. Now I have apps to play with and you've got my gears spinning about different experiments to try. Thanks!