ball() : position(0.0), velocity(0.0), radius(BALL_RADIUS), mass(BALL_MASS) {
        index = ballIndexCnt++; Reset();
}

ball(){
    position(0.0);
    velocity(0.0);
    radius(BALL_RADIUS);
    mass(BALL_MASS);
    index = ballIndexCnt++; Reset();
}