var len;

var angle;

var angularVelocity;

var damping;

​

function setup() {

  createCanvas(400, 400);

  len = 100;

  angle = 0;

  angularVelocity = 0;

  damping = .99;

}

​

function mousePressed() {

  angle = atan2(mouseY, mouseX);

}

​

function draw() {

  background(51);

  angle = angle + angularVelocity;

  angularVelocity = angularVelocity + (sin(angle) / len);

  angularVelocity *= damping;

  stroke(220);

  translate(width / 2, 10);

  rotate(radians(-90));

  var x = len * cos(angle);

  var y = len * sin(angle);

  line(0, 0, x, y);

  ellipse(x, y, 10);

}