Correct option is D
In an
unlubricated journal bearing,
dry friction occurs because there is
direct contact between the journal (shaft) and the bearing surface without any lubrication to reduce the friction. Dry friction arises when two solid surfaces slide or attempt to slide against each other, and it results in higher frictional resistance compared to lubricated conditions.
Fluid friction occurs when a
lubricant (liquid or gas) is present between two surfaces, forming a film that prevents direct contact. Since the journal bearing in this case is
unlubricated, fluid friction does not occur.
Rolling friction occurs when one surface rolls over another, such as in ball bearings or roller bearings.
In journal bearings, the shaft slides against the bearing surface rather than rolling, so rolling friction does not apply here.
Sliding friction occurs when one surface slides over another with some form of lubrication or minimal resistance. While sliding does occur in a journal bearing, the term "dry friction" is more accurate when there is no lubrication.
