Mechanical losses in a synchronous motor include:

Concept:

Iron losses

Iron losses or core losses  includes both hysteresis and eddy current losses.

Hysteresis losses:

These are due to the reversal of magnetization in the transformer core whenever it is subjected to alternating nature of magnetizing force.

Eddy current losses:

These are basically I2R losses present in the core due to the production of eddy current in the core.

Iron losses = Eddy current + Hysteresis losses

Mechanical losses

Mechanical losses are caused by the movement of the motor.

These include the friction in the motor bearings, friction between the brushes and the commutator, and drag on the rotor caused by turbulence of the air around it. It is referred to as windage loss.

Mechanical losses = Friction + Wind age losses

Stray losses = Iron + Mechanical losses