Friction on an inclined plane

Nstraw

If we Are moving an object on an inclined surface than shouldn't friction be in the same direction?

Doc Al

Same direction as what? The motion of the object?

anjelin

Friction is always in the opposite direction to the direction of movement of an object.

arildno

Not exactly.
It opposes the RELATIVE motion the object has to say, the underlying surface.

That is:
Friction seeks to equalize the motions of the object and the surface.

Suppose you drop a brick (no horizontal velocity) onto a moving plank.
The friction from the plank will accelerate the brick in the direction of its own generated horizontal motion, until the brick moves with the same speed as the plank.

Nstraw

So friction will oppose the motion

arildno

It opposes relative motion between the object and the surface.