Returns the current force of the Tween, relative to straight linear motion being 0. The 'units' for this measure of speed are in units per duration. Numbers greater than 0 indicate an acceleration while numbers less than 0 show deceleration.
Force is often useful in determining Squash and Stretch, a common animation technique to convey a soft body.
This is identical to the current second slope of the easing shape function.
import megamu.shapetween.*; NEED EXAMPLE HERE
force()