Saturday, 10 March 2012

Tennis ball arc research

Thinking about spacing the tennis ball out so that it's not bouncing up and down in a straight line, I had a look back at some of the videos to try and get to grips with the pattern of the arcs after the ball first hits the ground.

Using the same videos as reference, I took the frames where the ball was at its lowest and highest points, dropped the transparency (acting as a sort of onion skin) and, from there, was able to loosely scribble the path of the arc that the ball took.

Forgive the horrible scribbly lines... I'm running Windows through an emulator which doesn't have native tablet support...!

Anyway, as you can see, the ball takes a sharp arc upwards but doesn't travel very far away from its original position. Each successive high point of the ball almost overlaps its previous downward path.

Slight difference in this one, the ball doesn't drop straight down after he drops it - presumably it's a bit windy or something - but usually, the ball will pretty much drop straight down, providing there's no other force acting upon it. The ball will be propelled slightly forward after its initial contact with the ground and will start to bounce away from its original position. Again, you can see it's quite a steep climb, but it doesn't really move very far away.

I also found this interesting image floating around online:

A stroboscopic/high-speed capture of... a bouncing tennis ball! It demonstrates the path of the ball very nicely... and you can even see the rotation. Interestingly, as the ball loses power, the arcs appear to get a bit wider and the ball travels slightly further. The bounce also appears to be a little slower, judging from the spacing, not quicker as I'd originally thought. (No idea why... thinking about it logically, it makes no sense. I suppose that if you just watch a ball being dropped because it's bouncing lower and lower it appears faster?)

Anyway! Very useful stuff, so hopefully I can now make a bold attempt at spacing out my animation and getting it to look a little nicer.

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