A logic level mosfet must have a threshold voltage <2volt.Silly advice.Leo..
@ted: it would conduct but RDS(on) would be pretty high,
I don't care about your opinion,First learn how to be a polite ........
to you in previous threads.
MOSFET works similar to NPN (2N2222).Arduino drives a voltage into the Gate thru 150 ohm resistor, (like R1),Source connects to Gnd,Drain connects to the 'bottom' of the motor.Rds of the MOSFET is very low, so the motor will see almost all of the battery voltage, vs the NPN wasting 0.7V across the Collector-emitter.