If I used an everyday 9v alkaline battery to power a 6v DC motor, would it work?
The speed of a brushed DC motor is roughly proportional to the voltage applied, given the same countertorque.

You are running the motor at 1.5 times the rated voltage, thus you get 1.5 times the speed.

There's a reason that motor is designed for 6V only. DC brushed motors are very forgiving, even the commutator and the bearing should stand 1.5 times the design speed for a long time.


But the gears don't.


It's most likely a plastic gearbox. Running it at overspeed will destroy the innermost gear very quickly. Don't do it.