class Ball {
  float x;
  float y;
  float w;
  float speed;
  
  Ball(float x_, float y_, float w_) {
    x = x_;
    y = y_;
    w = w_;
    speed = 0;
  }
  
  void gravity() {
    //add gravity to speed
    speed = speed + gravity;
  }
  
  void move() {
    //add speed to y location
    y = y + speed;
    //if square reaches bottom, reverse speed
    if (y > height) {
      speed = speed * -0.95;
      y = height;
    }
  }
  
  void display() {
    //dispaly circle
    fill (255);
    noStroke();
    ellipse(x, y, w, w);
  }
}