iPhone Accelerometer Values

Question

My question is about the iPhone accelerometer. Does the accelerometer measure acceleration or movement of the iPhone? What I mean is if I hold the iPhone and go from 0mph to 60mph, I would expect the measure of acceleration to increase in value from 0 to 60, but once I reach 60, I expect the value to return to 0 since I am "no longer accelerating" but am moving at a constant speed. Now if the accelerometer measure motion, I would expect it to register 0 to 60 and continue to provide a change in value as I move forward at 60mph. Sorry, I looked at a few books, programmed some code (values seemed to small to give a recognizable result over short distances or speeds), and a lot of web searches, and I am trying to get an answer to this question.

Thanx!

Answer 1

I think that the following links can clarify what the accelerometer of the iPhone does, and does not:

http://electronics.howstuffworks.com/iphone-accelerometer.htm

http://www.engadget.com/2012/05/22/the-engineer-guy-shows-how-a-smartphone-accelerometer-works/

Answer 2

A couple of points:

• The accelerometer never reads zero because gravity is always with us and is an acceleration (and a good thing too). If it ever reads 0 you are in deep doo-doo - you have been cast adrift in space, or else you are in free-fall plunging towards the ground.

• When you go from 0 to 60, acceleration does not "register 0 to 60". That isn't what acceleration is. It isn't speed; it's the rate of change in speed. Is this a Lamborghini or a VW Bug? They both go 0 to 60 but the acceleration might be very, very different.

  You might need to read a little physics textbook here, but to make it simple, think of it as how hard you are being pressed back against the car seat! If you are not being pressed back, thrown from side to side, etc., then your horizontal acceleration is zero even you are going 100 miles per hour.