What are the purpose of down feathers on a bird?

Birds need feathers or wings because a bird without wings they may get in danger and will not be able to eat do you know an opposum it can eat a bird or eagle

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