How does this only have 4,700 views? This was so intuitive and helpful. I'm a year out of college with my BS and not once in my entire educational career has anyone ever explained this. This is SUCH a useful context.
One radian is the angle span of an arc that's the same length as the radius. An angle in radians is a ratio of how many times longer an arc length is than the radius of the circle it's from. When the arc is a full circumference, that's 2π radians (because the whole circumference is 2πr). Since a radian is a ratio of two lengths, it's technically "unitless."
