friction

kitka, ongelma, konflikti, erimielisyys The rubbing of one object or surface against another.
(quote-magazine)
conflict Conflict, as between persons having dissimilar ideas or interests; clash.
(quote-journal)
puhekieltä: A force that resists the relative motion or tendency to such motion of two bodies in contact.
1839, (w), A Compendium of Astronomy Page 95

Secondly, When a body is once in motion it will continue to move forever, unless something stops it. When a ball is struck on the surface of the earth, the friction of the earth and the resistance of the air soon stop its motion.