An Acoustic Demonstration of Galileo's Law of Falling Bodies
  An acoustic method is presented for analyzing the time of falling motion. A ball is dropped from a measured height. The dropping device makes a distinct sound a well-determined time (roughly 14 milliseconds) after release. The ball subsequently makes a second distinct sound when it hits the surface below. These sounds are captured with a microphone resting on the surface and are readily apparent in the acoustic waveform. At each height (0.25m, 0.50m, 0.75m, and 1.00m), the measured drop time agrees with the drop time predicted by the law of falling bodies with a typical accuracy of 4.3 ms. 
Michael Courtney, Elya R. Courtney
physics.pop-ph physics.class-ph