What is water that flows across eatlrtus surface

Water that flows across the surface is called a;

Runoff

That's when rain has saturated the ground to the point it cant hold anymore and it runs over the surface.

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.