Acceleration minus acceleration from rotation

Geoff Canyon gcanyon at
Wed Feb 11 13:18:50 EST 2015

On Wed, Feb 11, 2015 at 11:59 AM, Richmond <richmondmathewson at>

> What my iPad CANNOT do, is detect if it is moved across a surface, for the
> very SIMPLE reason that it doesn't have
> "little wheels" or other motion sensors on its underside [ err . . .
> backside?].

AccelerationChanged delivers an X, Y, and Z parameters. If your cat slides
the iPad perfectly to the right, you should see that two of the parameters
(Y and Z?) stay at 0, but one of them (X?) changes, first to one sign
(positive?) and then the other (negative?) as the iPad slows to a stop. If
you're clever you can work out how far the iPad moved.

To the larger question, rotationRateChanged also comes in X, Y, and Z
params. Working out the math to isolate one from the other is indeed an
interesting problem.

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