what is the difference between a dc motor and an ac motor?
An induction motor uses a shorted rotor, and gets it's drive current to create the repulsion needed to make it turn. A DC motor is built to create the repulsion needed by virtue of the configuration of how the electromagnets are oriented in the motor. The problem with your question is that in a universal motor, it will run off of either AC, or DC voltage because it uses a commutator.
There are many types of both so it cannot be expained easily the differences. DC - Commutator (shunt, series and compound wound), Permanent magnet. Brushless. AC - Induction (3 phase and many different single phase types), Synchronous, Wound rotor, NS (induction regulator), Generally dc tends to have higher maintenance issues (motors tend to have brushes) and is less used than it was. Years ago it was easier to control the speed of a dc motor but modern variable drives mean that ac is often preferred.
