>> > I beg to disagree. If you are talking about acceleration of the sensor >> > itself then you'll see that: 1. it's not actually accelerating if you >> > attach a reference frame to the Earth (the freerunner is laying >> > still). 2. The gravitational force applied to the sensor is directed >> > to the center of the Earth, >> > > OK untill here. > > OK >> > so the reported "acceleration" should be positive too. >> > > The reported acceleration is positive, this is a fact (cat /dev/input/event3). > The question is : is a positive acceleration accelerating downward or upward ? > > The wiki tells that a positive acceleration is downward (Z axe pointing down). > This is not true, in my opinion. > > When standing still, the accelerometer must report an acceleration directed > in the > _oposite_ direction the the gravitational force. As it is reporting a positive > acceleration, then the Z axe goes up. > > And I believe the other axes are inverted as well (which, as suggested by > Michael, > is easily provable by turning the FR around so that each axes points down). > > What is drawn in the wiki is a reference system; in that reference system the gravity acceleration take the right sign, being in the same direction as the z axis. If you accelerate upwards your phone (with the screen pointing up) with an acceleration a you see a greater acceleration a_tot (along the z direction) that is the sum of gravity acceleration g and your imposed acceleration a (a_tot=a+g). That means that the force acting on the phone is equal to the mass of the mobile m time the total acceleration and you can verify it with a dynamometer.
Giacomo -- /_\ The ASCII Per comunicare in modo riservato: \_/ Ribbon Campaign gpg --keyserver pool.sks-keyservers.net \ X Against HTML --recv-keys 20611EAD /_\ Email! ---------------------------------------------------------------------- Please avoid sending me Word or PowerPoint attachments. See http://www.gnu.org/philosophy/no-word-attachments.html _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community