Condition-reasoning gravity puzzle!

All you can do is manipulate gravity.
Each stage has a number of circles, which grow larger under certain conditions.
But the conditions are different for each stage, and you have to guess each time.
If you can make all the circles bigger, you have cleared the stage.

You can guess the conditions of stage 1 just by watching the play movie above.
This should give you some idea of how the game works.

There are only 8 stages, but all of them are not easy to solve.
Even if you are familiar with puzzles, it will probably take you an hour to clear all of them.

If you like puzzles, please give it a try.