when we have a mass on an incline why do we have to break the weight into components?

Question

anonymous · Answer

We need to determine the fraction of the object's weight that is parallel and perpendicular to the surface. This is because ONLY the portion that is parallel to the surface can create motion down the incline plane and ONLY the portion that is perpendicular to the surface contributes to the normal force, which is important in friction force calculations.

anonymous · Answer

does tension have an opposing motion?

anonymous · Answer

Tension can either be directed in the direction of motion or opposite of the direction of motion. Take this for example. |dw:1332384041010:dw|The force F moves both blocks 1 and 2, the tension force acts in the opposite direction of the motion if we look at a free body diagram of block 1, while the tension acts in the same direction of motion for block 2. 

Friction ALWAYS opposes motion.