Physics

[Sean Panting]

Hello... im trying to make a game for my java programming class at school because of an assignment... anyways... its a game where you have to get the bouncing ball thru a hole in the wall, something like pong. well, ive got it all pretty much figured out... the problem im having is the physics on the ball. i did research on this already, and after some testing, created a class Ball that worked well for my other bouncy ball related game, but not this one. here's the code for class ball:

class Ball
{
    int x,y,diam;//starting coordinates and diameter
    double xspd,yspd,fric,grav;// x-axis speed, y-axis speed, friction, gravity
    Rectangle rect;//the bounding rectangle that is used to check for collisions with this instance
    Dimension dim;//set to the dimensions of the screen for checking for collisions with the edges of the screen
    Random rnd;//used to generate the random color
    Color col;//the color used to paint the ball
    public Ball(int x,int y,double xspd,double yspd,double fric,double grav,int diam,Dimension dim,Random rnd)
    {
        this.x = x;
        this.y = y;
        this.xspd = xspd;
        this.yspd = yspd;
        this.fric = fric;
        this.grav = grav;
        this.diam = diam;
        this.dim = dim;
        rect = new Rectangle(x,y,diam,diam);
        this.rnd = rnd;
        col = new Color(rnd.nextInt(255),rnd.nextInt(255),rnd.nextInt(255));
    }
    public void draw(Graphics g,Rectangle r1,Rectangle r2,Rectangle o)
    {//uses the graphics from the buffered image to paint the ball to the screen, and passing on 3 rectangles
        g.setColor(col);
        g.fillOval(x,y,diam,diam);
        calcXY(r1,r2,o);
    }
    //calcXY does just as it says... calculates the new x and y coordinates
    //also, the three rectangles passed on are the positions of wall1, the opening between the two walls, and wall2
    public void calcXY(Rectangle r1,Rectangle r2,Rectangle o)
    {
        if(yspd>=15)
        {
            yspd = 15;//limits the yspd so that it doesnt get over 15
        }
        if(y-diam>=dim.height||y+diam<=1)
        {
            yspd*=-1;//if it touches the top or the bottom of the screen, taking in account for diameter of the ball(thats where the //dimension comes in) then reverse directions
        }
        if(x-diam>=dim.width||x+diam<=1)
        {
            xspd*=-1;//same thing as above, but for the x axis
        }
        if(rect.intersects(r1)||rect.intersects(r2)&&!rect.intersects(o))
        {
            xspd*=-1;//if it touches wall one or wall two and does not touch the opening, reverse directions
//i did that so that the ball wouldnt just bounce off the opening between the two walls, like it did before i integrated the opening rect
        }
        if(fric>=3)
        {
            fric = 3;//dont mind this... this was something i put in to test something out
        }
        x+=xspd-fric;//what calculates the new x coordinate
        y+=grav+(yspd+=grav-fric);//what calculates the new y coordinate
        rect.setLocation(x,y);//set the new location of the bounding rectangle to properly check for collisions
    }

this actually works kinda fine. the ball actually works like a real ball... it starts going sideways, then goes more downward, and bounces off the bottom of the screen, and basically does an arc. it works, except the fact that each successive bounce is the same height as the one before. and there are probably other flaws to. but it still kinda works, for my needs. but its not random enough. the path of the ball is the same, it iterates 3 different paths, then starts over. i need the ball to be much more random. just for clarification, it follows the same arc every time, and the drop angle, thats the same every time, is wats causing the ball to not go thru the hole in the wall. if somebody could help me out, that would be great, thanks.

[Marek Krzeminski]

If your ball keeps going to the same height with each bounce then there must be a problem with your friction calculation, or the friction is too low.

Have a look here: http://www.marek-knows.com/downloads.php5?vmk=physics5a and compare the equations that I derive with what you have implemented.

For added randomness, each time the ball hits something, use a random number generator to "slightly" deviate the direction which the ball should go in so that the motion is more random!

[Mike Simmons]

It looks like your friction is always pointed in the same direction: -x and -y. Upward and to the left, I guess. So the ball slows down when it's falling downwards, but speeds up when it's moving upwards. You need the friction to change direction to always be opposite the direction of motion.