In some cities, air pollution is so bad that people wear masks to protect their respiratory systems when they go outside. What do you think are some
consequences of this degradation of the atmosphere?

Retype the question .

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