🔍 Key Concepts

• lubrication of ball bearings and how grease behaves inside a rotating bearing • difference between proper fill percentage and overpacking a bearing • effect of churning friction on bearing temperature

💭 Think About

• Think about what happens to grease when the bearing is spinning at speed: where does the grease go and how does that affect heat? • Which option describes a normal/acceptable operating condition, and which describes a condition that would cause excessive friction? • Is a bearing more likely to run cool when grease can circulate, or when there is no room inside the bearing for grease and rolling elements to move?

✅ Before You Answer

• Identify which choice describes a bearing that is overpacked with grease rather than properly filled. • Ask whether “designed high speed” and “long time in use” are necessarily abnormal or unsafe by themselves. • Check which option would cause the grease to churn with no space to move, creating extra friction and heat.