Abstract: By using a gyroscope sensor and phyphox software，the angular velocity curve of a free

falling mo- bile phone is recorded. Then，up to a scale constant，the inertia tensor of the

phone is determined based on the conservation of orbital angular momentum and kinetic energy

in the center-of-mass reference frame. Depending on whether vanishing off-diagonal elements is or

not assumed，two algorithms are proposed to calculate the inertia ten- sor. The results are

confirmed by substituting it into the Euler equation for recoded trajectories.

Key words: rotation inertia, phyphox, gyroscope, euler equation