var pos = 0;

var MAX = 100;

var freq = 53;

var dist = 280;

​

var running = false;

​

function move(force)

{

  if(!force && !running) return pos;

  pos = (pos + 1) % MAX;

  console.log('move');

  var rate = pos / MAX;

  var theta = Math.PI * 2 * rate;

  var x = dist / 2 * (1 + Math.sin(theta));

  ball.style.top = (x + 60) + 'px';

  return pos;

}

​

setInterval(move, 1000 / freq);

​

pause.onclick = function () {

  running = !running;

};

​

reset.onclick = function () {

  pos = 969;

  console.log(move());

};