friction (FORCE) noun [U]
 the force which makes it difficult for one object to slide along the surface of another or to move
 through a liquid or gas
 The friction on/against the ball's rough surface stopped it going very fast.
 Friction within the pump caused the metal to become hot.

 frictional  adjective
 

friction (DISAGREEMENT) noun [U]
 disagreement or unfriendliness caused by people having different opinions
 Politics is a source of friction in our family because we all have different views.
 Border clashes have led to increased friction between the two countries.
 I had a bit of friction with my teacher yesterday.