let scl = 0.02;

let protonRadius = 0.8414; // in fm

let electronMass = 0.9109; // in ap kg

let charge = 0.1602; // in aC

let constant = 8.987; // in Gkgm^3s^-2C^-2

let v = 1; // in fm/frame

let iterations = 10;

​

function setup() {

  createCanvas(640, 360);

}

​

function draw() {

  background(255);

  push();

  translate(width / 2, height / 4);

  fill(255, 0, 0);

  stroke(0);

  strokeWeight(3);

  circle(0, 0, protonRadius / scl * 2);

  stroke(255, 255, 0);

  noFill();

  for (let i = -width / 8; i <= width / 8; i += width / 8 / 5) {

    let pos = createVector(i * scl, -height * scl); // in fm

    let vel = createVector(0, v); // in fm/s

    let acc = createVector(0, 0); // in fm/s^2

    beginShape();

    for (let steps = 0; steps < 100; steps++) {

      for (let it = 0; it < iterations; it++) {

        let mag = constant * charge * charge / pos.magSq(); // G * a * a / (f * f) = kN

        let force = p5.Vector.mult(p5.Vector.normalize(pos), -mag);

        let acc = p5.Vector.div(force, electronMass); // k / (a * p) = EP m/s^2

        vel.add(p5.Vector.div(p5.Vector.mult(acc), iterations));

        pos.add(vel);

        acc.mult(0);

      }

      vertex(pos.x / scl, -pos.y / scl);

    }

    endShape();

  }

  pop();

  noLoop();

}