Coordinate system is backwards on some emitters

[reststop]

Reviewing your conversion I was having trouble understanding what happens on the screen when adjusting some parameters.

It appears now that I've done further examination, the coordinates are identical to those in Apple's Fireworks example for OSX. On OSX, the bottom left corner is 0,0 and on iOS the top left corner is 0,0.

This means that values for rocket velocity should be -400, and the yAccelleration values should all be + (positive) instead of - (negative). The yAccelleration values are supposed to simulate gravity and thus need to be reversed.

Otherwise, great work on converting Apple's sample code to iOS.