var dx;

var vx = [];

var fx;

var y = [];

var dy;

var vy = [];

var fy;

var dt; 

var r;

var I;

let p = 2;

​

function setup() {  

  createCanvas(400, 400);

  I=2;

  dt = 0.0005;

  h=1/400;

  r=0;

  dx = 0;

  fx=0;

  dy = 0;

  fy=0;

  x[0]=200;

  y[0]=200;

  x[1]=200;

  y[1]=350;

  vx[1] =2000;

  vy[1] = 0;

  }

​

function draw() {

background(255,255,255,20);

noStroke();

fill(0);

text("Two Body Gravitational Problem: Elliptic Orbits.",50,50);

text("Sun fixed, Planet moving at distance r ",50,70);

text("Gravitational force on Planet scales with 1/r^2 directed to Sun.",50,90);

text("Explicit time stepping.",50,130);

text("Play with different intial velocities (vx) + time steps",50,110);

text("Test with other powers than 1/r^2",50,150);

text("red: Sun, blue: Planet, black: Gravitational Force",50,170);

fill(255,0,0,255);

ellipse(200,200,20);

for (var i=1; i<I; i++) {

 fx=0;

 fy=0;

for (var j=0; j<I-1; j++) {

  dx = x[i]-x[j];

  dy = y[i]-y[j];

  r = pow(dx,2)+pow(dy,2);

  r =sqrt(r);

  fx = fx - 1000*pow(100,p+1)*dx/pow(r,p+1);

  fy = fy - 1000*pow(100,p+1)*dy/pow(r,p+1);

} 

x[i]=x[i]+vx[i]*dt;

y[i]=y[i]+vy[i]*dt;

vx[i]=vx[i]+fx*dt;

vy[i]=vy[i]+fy*dt;  

fill(0,0,255,255);

ellipse(x[i],y[i],5);

}

stroke(0);

line(x[1],y[1],x[1]+(200-x[1])/pow(r/50,2),y[1]+(200-y[1])/pow(r/50,2));

}

​

​