let dvv;

let dac;

let xy;

let vv;

let acc;

let rr;

const xx = 200;

const yy = 20;

const GM = 200;

​

function setup() {

  createCanvas(400, 400);

​

  xy = createVector(xx, yy);

  vv = createVector(0, 0);

  acc = createVector(0, 0);

  dxy = createVector(12, 12);

  dvv = createVector(0, 0);

  dac = createVector(0, 0);

}

​

function draw() {

  background(220);

​

  noStroke();

  fill(40);

  circle(200, 400, 160);

​

  circle(xy.x - dxy.x / 2, xy.y, 4);

  circle(xy.x + dxy.x / 2, xy.y, 4);

  circle(xy.x, xy.y - dxy.y / 2, 4);

  circle(xy.x, xy.y + dxy.y / 2, 4);

​

  stepMotion();

  // console.log(vv.y);

  if (dxy.x <= 0 || dxy.y <= 0) {

    saveGif('tidal', frameCount - 1, {units:"frames"});

    noLoop();

  }

}

​

function stepMotion() {

  rr = 400 - xy.y;

  acc.x = 0;

  acc.y = GM / rr ** 2;

​

  dac.x = (-GM * dxy.x) / rr ** 3;

  dac.y = (2 * GM * dxy.y) / rr ** 3;

​

  vv.add(acc);

  xy.add(vv);

​

  dvv.add(dac);

  dxy.add(dvv);

}

​