Описание тега easing-functions
Easing is an important topic for anyone who wants to define a point on a computer screen and move an object smoothly to that point in fixed timeframe. Easing functions involve distance and time. Penner style easing functions are called with a value for the current time elapsed (since the start of easing), the current position of the object to be eased, the difference between the destination point and the current position, and the length of time allotted for the completion of the easing. Easing functions are the most commonly encountered and these are functions attributed to Robert Penner for moving objects smoothly from one on-screen position to another with the illusion of smooth acceleration, deceleration and mass. The original Penner equations can be found here:
Some interesting websites explore easing functions in more depth:
Upshots.org "Understanding Easing"