// CSE 142, Spring 2010, Marty Stepp
// This program simulates the dropping of two balls from various heights.
// It uses the displacement method we wrote in the MathFun class.

import java.awt.*;

public class Balls {
    public static void main(String[] args) {
        DrawingPanel panel = new DrawingPanel(600, 600);
        Graphics g = panel.getGraphics();
        
        // initial positions and velocities of each ball
        int ball1x = 100;
        int ball1y = 0;
        int v01 = 25;

        int ball2x = 200;
        int ball2y = 100;
        int v02 = 15;
        
        // acceleration due to gravity = 9.81 m/s^2
        double a = 9.81;
        
        // draw the balls at each time increment
        for (int t = 1; t <= 10; t++) {
            double d1 = displacement(v01, a, t);
            g.fillOval(ball1x, ball1y + (int) d1, 20, 20);

            double d2 = displacement(v02, a, t);
            g.fillOval(ball2x, ball2y + (int) d2, 20, 20);
            panel.sleep(200);
        }
    }

    // Computes and returns the change in position (displacement) of a moving
    // body with the given initial velocity v0 in m/s, the given 
    // acceleration a in m/s^2, over the given interval of time t in s.
    public static double displacement(double v0, double a, double t) {
        // v0t + (1/2)at^2
        double answer = (v0 * t) + 0.5 * a * Math.pow(t, 2);
        return answer;
    }
}