What does mobile phone accelerometers actually measure

[Shashwat Sher]

Hi Guys

I am using a mobile phone to collect some accelerometer data for my walking experiments. I know this topic is done to death but a specific answer that I have never got is what does mobile phone accelerometers actually measure? Do they give the acceleration due to all the forces acting on the mobile or do they provide only the physical acceleration with respect to the inertial frame? If it is the former, do you know any apps that provide the latter readings?

 

[phyzguy]

I don't really understand your question. How is "the acceleration due to all the forces acting on the mobile" different from "the physical acceleration with respect to the inertial frame" ? The accelerometer measures the total acceleration acting on the phone. If the phone is being accelerated then the phone's reference frame is non-inertial. In other words, if the phone is in free-fall, the accelerometer measures zero. If the phone is being accelerated by the sum of forces acting on it, then the accelerometer measures the net acceleration. Does this answer your question.

 

[A.T.]

what does mobile phone accelerometers actually measure?

Acceleration relative to free fall:
http://en.wikipedia.org/wiki/Proper_acceleration

 

[Spookee]

Indeed (thanks @phyzguy) if you get this then you get a key gist of (Einstein's) general relativity. So congratulations to the O.P. and anyone else tuned in?