Basic question for mechanical engineer

When a lever, pulley, etc changes the direction of work, how much energy is lost? Is the loss purely due to friction on the axis of rotation e.g. a bearing, flex in the parts, and acceleration, or is there something else at play?

What search term can I put in to the Google machine to read the basics of this topic?

 

Flex in the stranded steel cable or synthetic rope (due to the wires and strands moving past each other) results in friction losses as well. The losses can be reduced by upsizing the pulley diameter, to get a larger bending radius for the rope.