Finding Resistance of an electronic component

[MCCCLXXXV]

This may be a really dumb/easy question, but...
I have a computer fan that I'm trying to repurpose. The specs on the fan say DC12V, 0.25A.

I'm trying to model the fan in a circuit diagram because I want to 1) make sure i don't put too much current through it and 2) add a potentiometer to it to control the speed. Now, in order to find the effective resistance of the fan, I thought I would be able to simply use the V=IR equation and solve for R=12/.25=48ohms. But I hooked up an ohmmeter to it and it seemed like the resistance was no where near 48 ohms and jumped around a lot (mostly just went into overflow mode). What would be the proper way to model the resistance of the fan?

Thanks

 

[skeptic2]

The easy way is to measure the voltage across the fan and the current through the fan at the same time and then divide the voltage by the current. This will not have any correspondence to the value you measure with an ohmmeter.

When a motor is running it also acts a generator and generates a back emf that opposes the flow of current through the motor. The current through the motor will vary with load so any value you measure is only representative of the motor at that voltage and load.