I am totally new to electronics and don't know much but am trying to create a project that uses a 29rpm 6v DC motor. I was wondering if I were to use a higher voltage battery ( a 9v battery) would it be able to power the lower voltage motor?
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.