The ciliary muscles change the shape of the providing about 20% of the eye's focusing power.

The ciliary muscle is a circular ring of muscle that attaches all the way around the lens. This ciliary muscle can change the shape of the crystalline lens by stretching it at the edges.

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on