### DampingFactor of joint

I ~~cannot understand the description of dampingFactor in http://gazebosim.org/tutorials/?tut=ros_urdf#Links
"Exponential velocity decay of the link velocity - takes the value and multiplies the previous link velocity by (1-dampingFactor)." Is there any math to explain it?~~

I find the unit of ~~dampingFactor ~~damping coefficient referenced from http://gazebosim.org/tutorials/?tut=ros_urdf#Joints and viscous friction coefficient in the motor which is usually expressed as Bm is (N*m)/(rad/s), so are they the same physical ~~quantity?~~quantity? I want to simulate a servo motor, what value should the damping coefficient be?

If the dampingFactor = c and angular velocity = w, the damping force is c*w?