Left/right click or tap to add a random ball.
Middle click to remove a ball.
Press "D" or "Delete" to remove the last ball.
Press "C" to clear all balls.
Press "I" or click the left-top to toggle info.
Press "F" to toggle frozen.
Press "T" when frozen to tick once.
Press "A" to toggle air resistance.
Press "E" to toggle elasticity.
Press "G" to toggle gravity.
Press "↑" or "↓" to adjust e (restitution coefficient).
Press "H" to toggle help.