A ball that falls

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Bouncing ball</title>
  </head>
  <body>
    <canvas id="stage" width="480" height="320"></canvas>
    <p class="hint">Click the canvas to drop the ball again.</p>
  </body>
</html>