The smooth, rounded rocks and stones found on beaches are a result of a process called beach erosion and abrasion. Here's how it works:

* Waves and currents: The constant motion of waves crashing against the shore and the pull of ocean currents act as a natural grinding machine.

* Friction and impact: As rocks and stones are tossed about by the waves, they rub against each other and the beach floor. This friction and impact wear down sharp edges and protrusions.

* Sand and gravel: The beach itself is composed of smaller particles like sand and gravel. These act like sandpaper, further smoothing the rocks.

* Time: This process takes a very long time. The longer a rock is exposed to the forces of erosion, the smoother it becomes.

So, in short, the smooth rocks on beaches are formed by the relentless action of waves, currents, and the abrasive power of sand over time.