Ball speed measurement with smartphone

 The most simple and convenient ball speed measuring method is the shooting chronograph. Until my instrument arrives, I use my smartphone to measure ball speed.

Primary school physics: speed=distance/time. If we know, distance is 10 meters, then we just have to measure the time between the release and the target hit. It is possible with a smartphone: We take an audio record of the shot, then open the audio file in an audio editor, and read out the release time and the hit time.
The difference of the two times is NOT the ball fly time! Think of this: If the phone is at you while shooting, the sound of the release arrives to the phone in negligible time. But the sound of the target hit has to fly 10 meters. The velocity of sound is 330 m/sec, and time=distance/speed, so it takes 10/330=0.03 sec (30 msec) for the sound to arrive at the phone.

So, fly time=hit time-release time-30 msec. (If distance is 10 meters.)

Now, we can calculate: ball speed=10 meters/fly time. 

You can find free audio editors for your smartphone. I prefer working on my PC, and large monitor, so I email the audio file to myself, open it on my PC with the Audacity, free audio editor. Please find a screenshot below. You can see the vaweform, the start- and stop times.


Remarks:

We measure ball speed because we would like to compare bandsets, balls, etc. Actually the raw audio file times are just as good for comparisons, it is not necessary to calculate ball speed.

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