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var canvas = document.getElementById("scratch");

// canvas dimensions
var width = parseInt(canvas.style.width);
var height = parseInt(canvas.style.height);

// retina
var dpr = window.devicePixelRatio || 1;
canvas.width = width * dpr;
canvas.height = height * dpr;
canvas.getContext("2d").scale(dpr, dpr);

// simulation
var sim = new VerletJS(width, height, canvas);
sim.friction = 1;

// entities
var segment = sim.lineSegments([new Vec2(20, 10), new Vec2(40, 10), new Vec2(60, 10), new Vec2(80, 10), new Vec2(100, 10)], 0.02);
var pin = segment.pin(0);
var pin = segment.pin(4);

var tire1 = sim.tire(new Vec2(200, 50), 50, 30, 0.3, 0.9);
var tire2 = sim.tire(new Vec2(400, 50), 70, 7, 0.1, 0.2);
var tire3 = sim.tire(new Vec2(600, 50), 70, 3, 1, 1);

// animation loop
var loop = function () {
    sim.frame(16);
    sim.draw();
    requestAnimFrame(loop);
};

loop();

<canvas id="scratch" style="width: 800px; height: 250px; background: #000;"></canvas>