What happens when I suddenly stop the axis of an electric motor?
When you stall a dc motor you get stall current and this is usually several times full rated load current. Because the motor is no longer spinning, the natural back-emf isn't present and the full 9 volts is applied across the armature coil resistance. This resistance is undesirable (it represents a loss) when normally spinning hence it has a low value and stall current can be high.

If the battery is regarded as a source of voltage then power into the armature resistance is stall current squared multiplied by R. It can easily burn a motor but, for a  feeble little 9 volt battery, there's usually not a problem .

When you release the armature the current flow tries to maintain itself because of the armature coil inductance and this can generate a voltage spike. You can calculate this if you know the value of rotor inductance and snubber values.

I'm not going to extend my answer into AC  machines because this would take too much time.