double Acceleration (object obj, frame range_start, double range_size )

Return Value: The obj's average acceleration between range_start - range_size and range_start

Arguments:

Acceleration returns an item's average acceleration (change in velocity over time) over a given time sample. NOTE: this function does not return the instantaneous acceleration of the item (i.e. this function != f''(x) ). Instead you define a time sample by providing a frame and an interval length, then the velocity is calculated at the start and end of that interval and the difference is the average acceleration. For example, if you enter 15 as the frame number and 3.5 as the double, the function will calculate the velocity at frame 11.5 and 15 and the acceleration will be the difference of the two.

Example:

In this example, you are using the acceleration of a null to control the rotation of a second null.

Uses for this function are varied. For example, you could tie this expression to a master moving null of a fish and drive a faster or slower tail output based on the amount of acceleration or de-acceleration.