🔍 Key Concepts

• Difference between static balance and dynamic balance in rotating machinery • What it means for the center of gravity (CG) to lie on the axis/center line of rotation • How unbalanced forces show up when a shaft is at rest vs when it is rotating

💭 Think About

• Think about what happens if the center of gravity is NOT on the center line of rotation. Would the shaft tend to roll or settle to one position when at rest? • Is static balance concerned with behavior while the part is at rest or while it is spinning? How about dynamic balance? • For a crankshaft that has its CG on the center line, which type(s) of unbalance are eliminated, and which might still remain when rotating at speed?

✅ Before You Answer

• Be clear on the definition of static balance: how does a perfectly statically balanced part behave when supported on frictionless bearings? • Be clear on the definition of dynamic balance: what extra condition must be met beyond static balance for a rotating body? • Verify whether a CG on the center line alone is sufficient to guarantee both static and dynamic balance, or just one of them.