This application provides amusement for my 3 year old while we wait at restaurants. I would gather from that that any child from age 2 to 4 would be equally amused.

As the ball bounces against the walls, it leaves a tail behind which will eventually slowly disappear. When the ball hits a wall, it's acceleration is reversed and ever so slightly reduced (friction of course). It is possible to get the ball bouncing very fast. Holding your phone so that the ball rests in one corner will slow the ball down.

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