Angular velocity and linear velocity
This online calculator converts angular velocity to linear velocity for given radius
While I was watching kids on carousel I've thought about which speed did they have. I've decided that it is easy to find, all you need to do is just measure their revolutions per minute (n) and radius of carousel (R).
With revolutions per minute one can find angular speed - one revolution changes the angle by radians, thus per minute it is radians, and per second it is radians.
Radians per second is the angular velocity . Linear velocity is trivial, 1 radian corresponds to arc with length of radius, thus