🔍 Key Concepts

• Viscosity is a fluid’s resistance to flow (how "thick" or "thin" it is). • For most lubricating oils, viscosity changes in a predictable way with temperature. • Think about what happens to cooking oil or motor oil when it is heated versus when it is cooled.

💭 Think About

• Picture cold engine oil on a winter day compared to hot engine oil in a running engine: which one flows more easily? • If a lubricant needs to provide a film between moving metal parts as the machinery warms up, would engineers expect the oil to get thicker or thinner as it heats? • Eliminate any option that suggests viscosity does not change with temperature—does that match your real‑world observations?

✅ Before You Answer

• Be sure you understand that higher viscosity = thicker, flows more slowly; lower viscosity = thinner, flows more easily. • Mentally test each choice using a simple example: a bottle of oil from the refrigerator vs. warmed on a stove. • Confirm that the relationship you pick matches the general behavior of mineral lubricating oils used in engines and machinery.