Code

library_books<canvas id="canvas" width="200" height="200" style="background-color: #f9f9f9;cursor:pointer;"></canvas>

<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var y=50,
    speed=5,
    gravity=0.08,
    animation;

function draw() {
  ctx.fillStyle = 'rgba(255, 255, 255, .5)';
  ctx.fillRect(0,0,canvas.width,canvas.height);
  ctx.beginPath();
  ctx.fillStyle="red"
  ctx.arc(100, y, 15, 0, Math.PI * 2, true);
  ctx.fill();  

  speed+=gravity;
  y+=speed;

  if (y > canvas.height-15) {
    y = canvas.height-15;   //To limit the ball till the ground
    speed = -speed*0.6;     //To bounce back when touch the ground
  }  
  animation = requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function() {
  animation = requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function() {
  cancelAnimationFrame(animation);
});
</script>