A RIDDLE FOR YOUIn some situations, I oppose the motion

In other situations, I facilitate the motion

But, I always oppose

The relative motion

Between two moving surfaces.

Put some lubricant, and

I become small there.

Making the moving surfaces rough

I make the movement tough.

I may be –

Static, sliding, rolling

But whenever two surfaces are in motion

I am always there,

Tell me who I am!

Answer: Friction