Sine wave easing for more natural animations

One of the most difficult aspects of animation is making them feel natural. Linear animations can feel clunky and jittery, giving the user a less than satisfying experience.

How do we solve this? With the math of nature of course!

       function easeInOutSine(t, b, c, d) {
          return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
        }

http://robertpenner.com/easing/