Whistling is considered bad luck among mariners because it challenges the wind. where did this idea most likely come from?

The idea most likely come from superstitious belief. Superstitious belief refers to a widely held but irrational belief in supernatural influences which lead to either good or bad outcome. Some superstitions originated from traditions, stories, folklore, myth, legends, etc. The belief that whistling on board brings bad luck is one of the sailors' superstitions. 

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

I’m confused so sorry