why is gravity an example of scientific law?

Gravity can be an example of scientific law because of the fact that it has been proven over and over, again and again. While a theory is proven by evidence, it can be disproved. Laws rarely change. Although there are theories about gravity as well. The difference is a theory explains why it happens while a law lets us calculate a way to find what happened. In Newton's Law of Universal Gravitation, the formula will allow you to calculate the gravitational pull of the Earth and what ever you dropped for instance. However Einstein's Theory of General Relativity explains why whatever you dropped fell. So it depends what you mean by gravity being a law. It can be both depending on if your using it to prove something or to explain why that force occurs. :)