🔍 Key Concepts

• Viscosity as a measure of a lubricant’s resistance to flow • How bearing load (torque) and shaft speed (RPM) affect the lubricating film thickness • Difference between conditions that favor thicker oil vs thinner oil in machinery bearings

💭 Think About

• Think about what happens to the oil film between a bearing and a shaft when the shaft is turning slowly but carrying a heavy load versus turning very fast with a light load. • Ask yourself under which condition it is easier for the oil film to be squeezed out from between the bearing surfaces, and what that implies about the needed viscosity. • Consider how high rotational speed can help ‘pump’ a lower-viscosity oil into a stable film, and how low speed with high load might change that requirement.

✅ Before You Answer

• Identify which option correctly pairs high load / low speed or low load / high speed with a higher viscosity oil requirement. • Eliminate any choice that claims viscosity is unrelated to load and speed — is that realistic in real machinery? • Check which answer matches the idea that heavier loading and less hydrodynamic action generally calls for a thicker, more robust lubricating film.