1 Radian: Clear Definition

One unit of ANGLE or ARC MEASURE which you're probably familiar with is that of a "degree." One degree is 1/360th of a full revolution, right? Another unit of ANGLE or ARC MEASURE is a "revolution". 1 revolution = 360 degrees, right? Well, there is ANOTHER unit of ANGLE or ARC MEASURE with which you'll soon become familiar. This new unit of ANGLE or ARC MEASURE is called a RADIAN. Interact with the applet below for a few minutes. Reset it a few times and start the animation again each time. Be sure to change the circle's radius as you go along. After interacting with this applet, answer the question that appears immediately below it.
Again, recall that a "degree", a "revolution", and a "radian" are all units of ARC MEASURE (i.e. AMOUNT OF SPIN). Complete the following sentence definition: Definition: 1 RADIAN is defined to be a unit of ARC MEASURE for which.....