function BallSwing(fulcrumx, fulcrumy, ballx, bally, r){

    x = ballx - fulcrumx;
    y = bally - fulcrumy;
    this.poleLen = Math.sqrt(x*x + y*y);
    this.fx = fulcrumx;
    this.fy = fulcrumy;
    this.bx = ballx;
    this.by = bally;
    this.dx = 0;
    this.dy = 0;

    this.update = function(){
        x = this.bx - this.fx;
        y = this.by - this.fy;
        realLen =  Math.sqrt(x*x + y*y);
        nx = x/realLen;
        ny = y/realLen;
        this.dy += 1;
        s = this.dx * nx + this.dy * ny;
        this.dx -= s*nx;
        this.dy -= s*ny;
        dlen = this.poleLen - realLen;
        this.dx += dlen * nx;
        this.dy += dlen * ny;
        this.bx += this.dx;
        this.by += this.dy;
    };

    this.draw = function(){
        line(this.fx, this.fy, this.bx, this.by)
        circle(this.bx, this.by, r)
    };

}