Noun

(controversies)

A debate, discussion of opposing opinions; strife.

* {{quote-news

, year=2011 , date=October 1 , author=Phil McNulty , title=Everton 0 - 2 Liverpool , work=BBC Sport citation , page= , passage=The game was engulfed in controversy when Rodwell appeared to win the ball cleanly in a midfield challenge with Suarez. The tackle drew an angry response from Liverpool's players- Lucas in particular as Suarez writhed in agony - but it was an obvious injustice when the England Under-21 midfielder was shown the red card.}}

Noun

(-)

The rubbing of one object or surface against another.

* {{quote-magazine, year=2013, month=July-August, author=(Henry Petroski)

, title= Geothermal Energy , volume=101, issue=4, magazine=(American Scientist) , passage=Energy has seldom been found where we need it when we want it. Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame.}}

Conflict, as between persons having dissimilar ideas or interests; clash.

(physics): A force that resists the relative motion or tendency to such motion of two bodies in contact.

* 1839 , (Denison Olmsted), 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.