Learning Gravity, Basic Physics, and Camera Controls: An Angry Birds-like Game, Part I - Learn GameSalad for iOS: Game Development for iPhone, iPad, and HTML5 - page 169

Open the Projectile actor in the Actor Editor. Create a Boolean actor attribute
and name it ''HasBeenTouched.''
In the Touch rule, add a Change Attribute behavior above the Constrain
Attribute behavior. Change HasBeenTouched to true, as shown in Figure 6-13.
Figure 6-13. Changing HasBeenTouched attribute
Then add a Change Attribute behavior at the top of the Behaviors window so
that the HasBeenTouched attribute is reset to false when you initiate the scene.
Set Projectile.HasBeenTouched to false.
Then expand the Otherwise section of the rule and add a new rule in this
section. Name this sub-rule ''Throwing.'' The condition is ''Attribute''
''Projectile.HasBeenTouched'' is ''true.'' Then drag and drop a Change Velocity
behavior into the Throwing rule. Change the settings of this behavior to
 Direction: 180 + vectorToAngle(Projectile.Position.X-
gameInitialX, Projectile.Position.Y-gameInitialY)
 Relative to: scene
 Speed: 10*magnitude(Projectile.Position.X-gameInitialX,
Projectile.Position.Y-gameInitialY)
The rule is shown in Figure 6-14.