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enter image description here

The black lines are a table tennis table and a net from above. Red is the curve of a topspin with sidespin. Green is another one by the other player. In the moment green hits the ball, it is flying in the direction of the vertical blue line. The ball now flies in a curve because of the sidespin and eventually will change its direction to the horizontal blue line.

With no sidespin, α would be 180°. The more sidespin the green topspin has, the smaller α will be. With some sidespin, the angle will decrease.

You can see an angle that gets close to 90° here: https://www.youtube.com/watch?v=9XNhRxTUKq0

Now my question is: how small can α be?

  • What α could possibly be done by a human?
  • How small can α be if you could increase the spin to any amount of turns per minute?
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The first question is biology related. The second is pure physics or aerodynamics.

According to Wikipedia at https://en.wikipedia.org/wiki/Magnus effect the Magnus force, the sidespin force, is proportional to omega, the spin. If true the minimum alpha would approximate zero. But I am guessing there will be other effects like vertex effects and nonlinearities way before you get to that.

There's been more work on baseballs, soccer balls and golf balls, and they all have some seams, contrary to ping pong. They're also much heavier. See for baseball https://pdfs.semanticscholar.org/2df3/1d4256c29ae2ba973c7f7bd2f9a992cca848.pdf (but not an answer to your question, just some of the physics).

For ping pong, a similarly detailed paper at http://www2.hawaii.edu/~taha/physcompclass/final/final_revised.pdf

Maybe that can get you some realistic (biologically) numbers, and get you started calculating.

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