Who Am I Riddle

#162

In some situations, I oppose the motion 
In other situations I facilitate the motion but, 
I always oppose the relative motion between the two moving surfaces.
Put some lubricant and I become smaller making the moving surfaces rough, 
I make the movement tough I may be static sliding or rolling but whenever two surfaces are in motion I am always there. 
Tell me who I am.. 

  Difficulty Level - 2/5

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