I'm not much better informed regarding the phone ap but as recall I had to have GPS on and that they use the phone's built in accelerometers. I tend to expect that the younger types will be more aware of this tech and hope that we can work out whether the use is reliable.
I need to get my ap out and play with it to get up to speed again but not now as Rupert the house rabbit is bugging me for treats so will get no peace. :-)
Have a look and let me know what you think of the aps.
No speaka "aps," Normk!
Did not realize cell phones (all?) are equipped with accelerometers.
Differentiating distance vs. time gives speed (as our GPS receivers do); the second derivative, the rate speed changes, should yield acceleration. Reckon that's a doable do with a GPS receiver, but . . . unsure whether all cell phones have GPS receivers.
Regardless, intriguing possibilities and interesting subject Normk; thanks for raising it.
Back to measuring stopping distances, looks like using a GPS receiver to set the approach speed might be more accurate/convenient than using even a calibrated speedometer. While measuring distances is a drag, if distinguishable markers could be laid down and left in place for each trial, only one measurement from the starting point of the tests would be required.
The motorcycle magazines still use stopping distances when testing motorcycles, perhaps because this measurment has become a "convention," even though more precise and accurate measurement techniques and instrumentation are available.
Way leads onto way!
At least, SOME cell phones, apparently, have built-in accelerometers:
Just speculating; an on-board accelerometer (piece of hardware) may be more useful than GPS location-vs.-time differentiation to determine acceleration, because . . . the "Z," or vertical, component is the most difficult and least accurate of the axes determinable from navigation satellite ephemera; a geometric fact-of-life. Z-axis uncertainties may degrade acceleration data synthesized from GPS positioning information . . . DISCLAIMER: Speculation only, I have no evidentiary basis for the concept.