// -------------------------- Kick ----------------------------------------
//
// applys a force to the ball in the direction of heading. Truncates
// the new velocity to make sure it doesn't exceed the max allowable.
// ------------------------------------------------------------------------
public void kick(Vector2D direction, double force) {
// ensure direction is normalized
Vector2D d = direction.cloneVec();
d.Normalize();
// calculate the acceleration
Vector2D acceleration = d.multiply(force).divide(mass);
// update the velocity
velocity.cloneVec(acceleration);
}
