Explanation of a torque of friction in a bearing

[bolzano95]

Homework Statement

I have no idea what torque of a friction in a bearing is. I'm looking for good explanation.

Homework Equations

The Attempt at a Solution

I understand what torque/friction/bearing is. But I have no idea how they come together when looking at the actual mechanical problem. Help!

 

[CWatters]

Friction torque is just the torque needed to turn a shaft in a bearing (no other load)

In a plain bearing you have two surfaces sliding over each other. Friction between the two surfaces requires a torque to overcome.

In a ball or roller bearing the balls roll and have rolling resistance that requires a torque to overcome .

It's one reason your fidget spinner slows down (in addition to air resistance etc).