Final answer:
Rotational speed and operating temperature are indeed crucial factors in selecting appropriate oil or grease for bearing applications, as they directly influence lubricant's viscosity and its effectiveness in protecting bearing under various conditions.
Step-by-step explanation:
The statement that 'the two factors that control the selection of oil or grease for a bearing application are rotational speed and operation temperature' is generally true. Rotational speed and operating temperature are critical considerations when selecting a lubricant for bearings. At high rotational speeds, a lubricant with a lower viscosity may be necessary to reduce friction and prevent damage to the bearing. Conversely, at lower speeds, a thicker grease might be preferable for better adhesion and protection.
Operating temperature directly affects the viscosity of a lubricant. At lower temperatures, oil's viscosity is higher, which may prevent it from flowing well and adequately lubricating the engine parts. As temperature increases, viscosity decreases, meaning lubricants must maintain an adequate film thickness to protect the bearing surfaces even when they become thinner at higher temperatures.
Understanding the relationship between viscosity, temperature, and lubricity is crucial for selecting oils and greases in mechanical applications. For example, motor oils must perform under a range of temperatures from the cold winter to the heat of a desert to protect the engine components effectively. Therefore, it's vital to choose a lubricant that can maintain its lubricating properties across the expected range of operational conditions.