LACS09_BodyG.java

//BodyG.java    MrG 2012.0621 (work in progress)
public class BodyG
{
    private Vector r;
    private Vector v;
    private double m;

    public BodyG(Vector r, Vector v, double m)
    {
        this.r=r;
        this.v=v;
        this.m=m;
    }

    public void draw()
    {
        StdDraw.point(r.getX(),r.getY());
    }

    public void move(Vector force, double time)
    {
        Vector a = force.dilate(1.0/m);
        v = v.sum(a.dilate(time));
        r = r.sum(v.dilate(time));
    }

    public Vector getR()
    {
        return r;
    }

    public Vector pullFrom(BodyG other)
    {
        double G = 6.67e-11; //meter^3*kilogram^(-1)*sec^(-2)
        Vector deltaR = other.getR().diff(this.r);
        double d = deltaR.abs();
        double f = G*this.m*other.m/d/d;
        return deltaR.dilate(1.0/deltaR.abs()).dilate(f);
    }
}