  Acceleration sensors built into smartphones, i-pads or tablets can
conveniently be used in the Physics laboratory. By virtue of the equivalence
principle, a sensor fixed in a non-inertial reference frame cannot discern
between a gravitational field and an accelerated system. Accordingly,
acceleration values read by these sensors must be corrected for the
gravitational component. A physical pendulum was studied by way of example, and
absolute acceleration and rotation angle values were derived from the
measurements made by the accelerometer and gyroscope. Results were corroborated
by comparison with those obtained by video analysis. The limitations of
different smartphone sensors are discussed.
