Algodoo

as circles pass through the lasers, gravity increases or decreases depending on which laser hits more or less balls. This creates kind of a pulsating effect.

[s]If the scene's attraction goes below 0 or above 100, open a console (press `) and type:

scene.my.att = 30 (or any other number greater than 0 or less than 100)
[/s]

EDIT: Added an IF statement to automatically 'fix' < 0 and > 100 problem