Definition of "friction"

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.

2013 July-August, Henry Petroski, “Geothermal Energy”, in American Scientist, volume 101, number 4

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.

1839, Denison Olmsted, A Compendium of Astronomy, page 95

The frictions should at first be very gentle, and performed with a view to restore heat, and not to force the blood towards the heart, which in drowned persons is already too much distended with it.

1792, James Curry, Observations on Apparent Death from Drowning, Suffocation

The frictions are made at bedtime, on a limited portion of the body, and on one side only—the calf of the leg by preference, or the thigh, groin, or axilla. It is enough to continue rubbing for from three to five minutes at most.

1874 January 7, M. Panas, “Treatment of Syphilis by Mercurial Friction”, in The London Medical Record, volume 1, page 5

Thais have been watching for signs of friction between the armed forces and the monarchy—the country's two biggest sources of political power—since the death in October of Bhumibol Adulyadej, King Vajiralongkorn's long-reigning father.

2017 January 14, “Thailand's new king rejects the army's proposed constitution”, in The Economist‎

Once finances are stabilised, getting Crossrail finished is Byford's most obvious task. Late and over budget, it is causing unwanted headlines and friction between the London Mayor and the Department for Transport that both sides would rather live without.

2020 December 2, Andy Byford talks to Paul Clifton, “I enjoy really big challenges...”, in Rail, page 52