I personally understand gravity and EM being a physicist. I've studied them, know their applicability, where they work, where they don't. I know the equations, how to solve them, what the problems are. I've done the experiments, gotten "my hands dirty" with circuits and astronomical calculations.
Thus I feel I am justified in saying I don't believe in those concepts because I've actually worked with them hands on. I feel very justified in saying I know gravity and EM

I would not say the same thing about evolution.

I have not worked with it, I'm not familiar with the equations or taxonomy. I don't know where it is applicable, where it is not. I have no experimented with it nor have "gotten my hands dirty" working with it. I feel justified in saying I believe in it because other scientists, whom I trust and respect, say that it works. They purportedly used similar scientific methods, similar math, similar methodology for me to know gravity and EM and thus I''m justified that what they say is true. I would NOT however go as far as saying that I know evolution but would only go so far as to say I believe in evolution.

And there is the third viewpoint. Someone who has not worked with gravity, EM, or evolution. Someone that doesn't have any experience with the scientific method, doing experiments in any of these fields, has never worked on the equations, has never "gotten their hand dirty" doing science. I would say it's inaccurate to claim that that person believes in those fields because they have no basis to form that belief. Even more inaccurate would be to say that they know those subjects. Rather, I would say that person has faith in gravity, EM, and evolution, has faith that those fields do what they are told (but haven't worked out for themselves) because they are trusting what scientists tell them but have no personal evidence to support that trust and no realistic way to understand or challenge said scientists on what they say.

So in my viewpoint, unless you work in the field and have gotten your hands dirty, worked the equations, done the experiments, played with the concepts, then the most you can do is have faith in what others are telling you for you do not know. And if you have experience in one field of science, if you know one field of science, you can believe what other scientists are telling you for you have evidence that their methods work in your field and thus can justifiably claim that that same methodology works in other fields.

You should not make the mistake of conflating religious knowledge, belief, or faith with scientific knowledge, belief, or faith. That is part of the NOM philosophy. Just because these words have religious connotations DOES NOT make them uniquely religious. And realizing whether your support of science comes as knowledge, belief, or faith makes you better equipped to judge science and it's results. For if you know, you can be trusted that the ideas of science you promote are based on actual science; if you believe less so, you can be trusted that because you know one field you can comment on another; but if you have faith, you cannot be trusted to be an effective communicator of science.