Abstract: In the "Free Fall Motion" section of the "Do It" column in the 2019 edition of the "Senior High School Physics" textbook (Compulsory Volume 1) published by the People's Education Press, when using the phyphox physics workshop app to measure the acceleration of free fall, if the phone is placed horizontally with the screen facing up and released from rest, the graph will show a trend similar to a "ramp," with the measured value of acceleration gradually decreasing. After precisely determining the various parameters of the phone, the value of the drag coefficient CD for a smartphone falling horizontally was obtained using the simulation function of COMSOL Multiphysics software. By comparing hypotheses, theoretical derivation, software plotting, and comparative experiments, the main reason for the "ramp" effect was found to be air resistance.