Why does the ball deviate more on the second bounce ?

[ttmonster]

Hi ,

I am sure this might appear to be a naive question to some or most of you but I will still put it out there .... because this has been spinning in my brain for some time now :

1. Why does the table tennis ball deviate more when it hits the table the second time around ? Looking for a high school physics explanation if not some thing more simple

2. Why some topspins jump up from the surface while some of them skid through even though I am sure there was no sidespin on the ball ... can it happen normally .. or its just me or some thing external like sweat or may be a dead rubber on the opponents paddle ?


Always believed in asking stupid questions than remaining stupid ... so I am not scare if some of you are going to scold me

 

[schumi2]

Your brain appears to be working overtime but if you feel that you have noticed the ball moves more the second time, all well and good but I feel that if it did, your opponent may have put more on the ball than on the first shot thus it would be different. From my point, I would probably be concentrating in getting the ball back the first time rather than picking up what it might do on the second time. As for topspin, the ball should come off high if done well but sometimes it does skid probably due to a spot on the table but mainly this does not happen but can. I stand to be corrected on this.

 

[tpgh]

the ball slows down after the first bounce, so the deviation becomes more apparent (spin is still high, speed of ball becomes slower)

topspin skids if the ball trajectory is low while it will kick up if it is a high dipping loop

 

[ttmonster]

the ball slows down after the first bounce, so the deviation becomes more apparent (spin is still high, speed of ball becomes slower)

topspin skids if the ball trajectory is low while it will kick up if it is a high dipping loop

Thanks ... so first time the ball skids since force on the ball > force of friction ... next time force of friction > force on the ball so the deviation is more ... or something similar ...

And I guess it is similar reason for the 2nd case also ... the translational force on the ball with lower trajectory is more then the ball skids ... if it looped high the translational force is less and the friction generated from the the spin is more so it kicks ........

Thanks a lot for the simple explanation ... helped me understand .. hope I am right

 

[ttmonster]

Your brain appears to be working overtime but if you feel that you have noticed the ball moves more the second time, all well and good but I feel that if it did, your opponent may have put more on the ball than on the first shot thus it would be different. From my point, I would probably be concentrating in getting the ball back the first time rather than picking up what it might do on the second time. As for topspin, the ball should come off high if done well but sometimes it does skid probably due to a spot on the table but mainly this does not happen but can. I stand to be corrected on this.

... okay .. so what I meant is ... e.g when you do a ghost serve .. the ball does not come back on the first bounce but comes back on the 2nd or third bounce ... similarly you just put spin ( any spin ) without your opponent hitting it .. it deviates more from its original path on 2nd or 3rd bounce compared to the first bounce

 

[PandaMike]

This video may help explain that. It doesn't answer your question directly..but it shows that there might be different spins on the ball then you are aware of.

 

[PandaMike]

Heres the link.

 

[ttmonster]

Thanks Mikes the video was wonderful and insightful !!!
Even though it does not answer my question directly it definitely opens up the mind to the possibilities ...
So surely there is more than meets the eye .. I am sure there is a physics research paper lurking behind the dynamics in table tennis ... two almost rigid objects ... the table, a plane and the ball , a sphere and a very elastic plane .. the rubber .. mind boggling !

 

[chughtai]

this is a brain twister