Which statement describes a scientific law?

a law states how something behaves and explains why.
a law is a proven fact that cannot be changed.
a law changes based on new observations and testing.
a law is based on a single hypothesis or observation.

A law is a proven fact that cannot be changed.

When a hypothesis is tested repeatedly and gives out same results universally, then it becomes a scientific law. The difference between scientific theory is that it gives detailed explanation about how and why things  behave, the way they behave. On the other hand, a scientific law is just a statement that explains the behavior of natural phenomenons. A law is a proven fact that cannot be changed because it becomes law only after multiple times testing of the hypothesis.

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.