Usually, the only friction present in a DC machine is from the _________ and ________.

• A. Bearings / Brushes
• B. Bearings / Commutator
• C. Bearings / Windings
• D. Bearings / Pulleys

Answer: (A)

In a DC machine, the mechanical friction you encounter inside the machine mainly comes from two places: the bearings and the brushes. Bearings support the rotor as it spins, creating rolling friction that slows things slightly. Brushes are pressed against the rotating commutator to maintain electrical contact, and that contact involves sliding friction and wear. The windings themselves aren’t a source of mechanical friction—they’re electrical components, either stationary or rotating with the armature, but their function is conduction and magnetic interaction, not contact drag. The commutator isn’t friction by itself; the friction comes from the brushes rubbing on its surface. Pulleys, if present, are part of an external drive system and aren’t the internal friction source in the machine. So the usual internal friction is from bearings and brushes.