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Editorial Team
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Asked: 2026-06-02T01:31:32+00:00

I want to use the iPhones’s accelerometer to detect motions while driving. I’m a

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I want to use the iPhones’s accelerometer to detect motions while driving. I’m a bit confused what the accelerometer actually measures, especially when driving a curve.

Car driving a curve

As you can see in the picture, a car driving a curve causes two forces. One is the centripetal force and one is the velocity. Imagine the iPhone is placed on the dashboard with +y-axis is pointing to the front, +x-axis to the right and +z-axis to the top.

My Question is now what acceleration will be measured when the car drives this curve. Will it measure g-force on the -x-axis or will the g-force appear on the +y axis?

Thanks for helping!

UPDATE!

For thoses interested, as one of the answers suggested it measures both. The accelerometer is effected by centrifugal force and velocity resulting in an acceleration vector that is a combination of these two.

enter image description here

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1 Answer

  1. Editorial Team

    I think it will measure both. But don’t forget that the sensor will measure gravity as well. So when your car is not moving, you will still get accelerometer readings. A nice talk on sensors in smartphones http://www.youtube.com/watch?v=C7JQ7Rpwn2k&feature=results_main&playnext=1&list=PL29AD66D8C4372129 (it’s on android, but the same type of sensors are used in iphone).

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