A marsh ecosystem has a gross primary production of 17,500 kcal/m2 per year. If the energy
used for autotrophic respiration is 8,500 kcal/m2 per year, what is the net primary production
in this ecosystem?

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

Ican not answer this question since it does not have enough information