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PostPosted: 27 Jul 2018, 07:36 
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Also, is it the average speed measured from the bat to when it hits the table? Or is it the "instantaneous" speed an instant after the bat has hit the ball? Or some combination depending on how far the ball travels and how much time between frames on a video?

The reason I ask this is because I believe that the effects of air resistance / air friction are significant, otherwise someone would be able to hit a table tennis ball more or less as far as a golfer can hit a golf ball.

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PostPosted: 27 Jul 2018, 23:06 
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The way we were forced to calculate this based on a frame count over a known distance it amounts to an average of the speed.

When it is done with a radar gun it is also an average (because the gun takes several measurements to make sure one is not an aberration or machine artifact) but these are taken over a much smaller interval so approximate an instantaneous measurement.

Note: It turns out due to issues surrounding the definition of precision and significant digits no scientific measurement is ever purely different from an average of some sort.

No whether it is right off the bat or half way down the path or at the end of the flight would depend on where the device was aimed or focused. My bet it is not right off the bat since the motion of the bat and its much larger cross section would make it harder to rule out motion from it, but engineers do amazing things sometimes, so it is possible.


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PostPosted: 28 Jul 2018, 05:47 
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Apologies all around, fellow table tennis junkies, I forgot I even posted this!!!! So I just read all the comments yesterday and was so alarmed that I went back to the room I took the footage in, got the height of several objects in the background and made sure everything was placed exactly as it was the night I shot this video which took literally an hour since I had to compare the footage of a new shot to the old shot in an editing program! PHEWPH!!!!!! Turns out the video was shot in 60fps NOT 120fps for which I apologize wholeheartedly!!!!!!! It was not my intention to mislead anyone, I shot footage in both frame rates that night and I uploaded a different video than intended and then went right on ahead with my analysis once it was uploaded on youtube. Let this be a lesson to all that sleep deprivation = SLOPPY WORK!!! The frame rate can be verified by realizing that the zenith of the ball height is 1.5 feet and is reached 20 frames after the bounce . The 1.5 feet makes sense considering I'm 5'6", the table is 2.5", I am bent over and 2 feet behind the ball and even in the forced perspective the ball only reaches my sternal angle which is 12.75 inches from the top of my anterior skull (to say nothing of my massive posterior/occipital cranium, hahahaha).

That said, I then felt the need to go back and analyze the film using software I have used as a TA in the past (I have a PhD in Physical Chemistry in case anyone was wondering just what the hell I TA'd for, hahaha). Here are the official measurements:

Length of table traversed by shot = 8.95 feet
Width of table traversed by shot = 4.08 feet
Height traversed by shot = 1.28 feet
Total estimated distance travelled is = 9.92 feet

Frame speed is 60 frames per second
Frames required for ball to travel 9.92 feet is 6.2 frames

(9.92 feet/(6.2/60 seconds))*(60 seconds/1 minute)*(60 minutes/1 hour)*(1 mile/5280 feet) = 65.5 mph average velocity over the course of the shot.

In the first 2 frames the ball travels 4.8 feet (according to analytics software, anyway…) which means that the average velocity over the first 4.8 feet is 98 mph. It's impossible to achieve a good estimate of the instantaneous velocity with this video quality and the software I have, but suffice it to say that it's over 98mph. Again, total apologies for the original sloppy maths—hope this clears everything up!!!

As for why it's much easier to hit the ball faster with this grip than a standard shakehand, it's the biomechanical equivalent of throwing a baseball with good form vs. the colloquial "throwing like a girl" which is to say the former releases a series of stacked levers in a whip the towel motion while the other is a single fixed arm swung around a single joint (see the fixed arm technique swinging around the shoulder joint in Dima's smash, for instance). My paddle has evolved well past where it is in this video and it's nice to look back at this video as a stop along the way. :)

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