The other source of friction is the bearings supporting the _________ _____.

• A. armature shaft
• B. rotor
• C. stator
• D. end bell

Answer: (A)

Friction in a rotating machine comes from the parts that actually move and the supports that allow that motion. The bearings are there to support the rotating part, which is the armature shaft. As the shaft turns, the bearing surfaces, lubrication, and the interaction between the rollers or balls create bearing friction. This is a distinct source of resistance from other forms like windage or brush contact, so the bearings supporting the armature shaft are the correct source described. The rotor and stator are the stationary and rotating magnetic assemblies, respectively, and the end bell is just the housing for the bearings—not the component being described.