In a DC machine, which components are typically the source of mechanical friction?

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Multiple Choice

In a DC machine, which components are typically the source of mechanical friction?

Explanation:
Mechanical friction in a DC machine comes from parts that actually move and rub against each other. The shaft is supported by bearings, and as it spins these bearings create friction, which is a normal mechanical loss. The brushes, which remain in sliding contact with the rotating commutator to carry current, also produce friction and wear due to that sliding contact. Winding copper losses are electrical (I^2R losses) and don’t contribute to mechanical friction. The commutator itself isn’t a separate friction source—the friction comes from the brush contact with it. External drive components like pulleys are not part of the machine’s internal mechanical friction. So bearing friction together with brush contact friction is the typical source of mechanical losses in a DC machine.

Mechanical friction in a DC machine comes from parts that actually move and rub against each other. The shaft is supported by bearings, and as it spins these bearings create friction, which is a normal mechanical loss. The brushes, which remain in sliding contact with the rotating commutator to carry current, also produce friction and wear due to that sliding contact.

Winding copper losses are electrical (I^2R losses) and don’t contribute to mechanical friction. The commutator itself isn’t a separate friction source—the friction comes from the brush contact with it. External drive components like pulleys are not part of the machine’s internal mechanical friction.

So bearing friction together with brush contact friction is the typical source of mechanical losses in a DC machine.

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