Why are some rocks smooth and others are not?

Rocks can become smooth through processes like erosion, where constant rubbing or flowing water wears down their surfaces over time. On the other hand, rocks that are not smooth may have experienced less weathering or have a composition that is more resistant to erosion, resulting in a rougher texture. Factors such as the type of rock, environment, and exposure to weathering elements play a role in determining whether a rock ends up smooth or not.