function setup() {

  createCanvas(500, 400);

  s = createSlider(-PI * 2, PI * 2, 1, 0.01);

}

function x(t) {

  return 0.25 * t * t * t * t - 200;

}

function xprime(t) {

  return Math.pow(t, 3);

}

function y(t) {

  return 50 * sin(t);

}

function yprime(t) {

  return 50 * cos(t);

}

​

function draw() {

  {

    push();

    translate(width / 2, height / 2);

    scale(1, -1);

    background(10);

    noStroke();

    colorMode(HSB);

    for (let t = -2 * PI; t < s.value(); t += 0.1) {

      const slope = sqrt(Math.pow(yprime(t), 2) + Math.pow(xprime(t), 2));

      fill(slope, 255, 255);

      circle(x(t), y(t), 5);

    }

    pop();

  }

  fill(255);

  textSize(20);

  text("t = [-2π ," + round(s.value() / PI, 2) + "π]", 10, height - 20);

  text("x(t) = .25t⁴ - 200", 10, 20);

  text("y(t) = 50sin(t)", 10, 50);

  text("Δt = .1", 10, height - 40);

}

​