How a magnetic field produces torque in a simple DC electric motor?

Question

How a magnetic field produces torque in a simple DC electric motor?

Answer 1

Static fields oppose the rotary field of the rotor. The 2 fields push against each other, and the motor spins. This force of opposing fields generates the "twisting" force of the motor, which is what torque actually is, it is a twisting, or turning force.

Answer 2

By the use of internal and external commutation  to create an oscillating AC current from the DC source -- so the DC motor is not purely a DC machine in a strict sense.

Answer 3

Magnetic inductance in the coils of wire in the motor produce a magnetic field. The magnetic field applies a force on the rotor. This force translates into torque on the motor load.