Chinese physicists used an acoustic stopwatch on a smartphone to measure the free fall constant. You can repeat the experiment at home.

In principle, you can calculate the free fall constant just knowing the school formula. It is only necessary to measure the coordinates and time of the beginning and end of the fall of the body. However, measuring time is not such a simple task here. Accuracy will be lost if you turn the stopwatch on and off manually.

That’s why physicists suggested using the “Acoustic Stopwatch”. This option has an app to access phyphox smartphone sensors. The stopwatch starts working as soon as a loud sound is heard in the microphone of the device. The same signal stops the stopwatch.

The scientists placed a steel ball on the end of a thin strip of wood protruding from the edge of the table. If you carefully hit the strip with a metal ruler, you can simultaneously send the ball into free fall and make a loud noise. The sound of the ball hitting the ground will stop the stopwatch.