What effect does friction have on the motion of a block on a surface?

Friction is a force that arises when two surfaces are in contact with one another, and it plays a critical role in the motion of objects. In the case of a block placed on a surface, friction acts in the opposite direction of the block's motion.

When the block is pushed or pulled, friction resists this movement, effectively opposing the applied force. This opposing force reduces the speed of the block or may prevent it from moving altogether if the frictional force is greater than the applied force. Therefore, the primary effect of friction is to impede motion, which is exactly why the correct answer indicates that friction opposes the motion of the block. Understanding this concept is essential for analyzing dynamics in physics, as it reveals how friction interacts with forces to determine the resulting movement of objects.