this.get("Friction").valueScale = 40
var g = this.get("Gravity"),
friction = this.get("Friction"),
ground = this.get("Ground"),
ball.getPosition().equals(ball.getPosition().addPt(pt(
0, ball.velocity * system.dt * s
ball.velocity == (ball.velocity +
g.getScaledValue() * system.dt -
((ball.velocity > 0 ? 1 : -1) * friction.getScaledValue()));
callback: (function() { ball.velocity = -Math.abs(ball.velocity); })
ground.getPosition().y <= ball.getPosition().y