We all believe in "assumed truths." Assumed truths meaning beliefs, doctrine, or just pieces of information we learned from people who don't know what they're talking about.
Gravity is actually a good example, actually. Scientists have done experiments, produced theories, and everything necessary to make a law out of it. I have not done these things. I have learned the basic laws of gravity and even have been taught some at the particle level, but I do not clearly understand it. Even worse, I haven't tested what I assume to be true. In fact, I'd say 99.9999% of people haven't tested the laws of gravity for themselves.
How are we supposed to know that their tests are accurate?
How do we know they didn't skew the results to fit their theory?
How do we know that the test results haven't been misinterpreted by the few that have done them?
There are a lot of ways to explain gravity and some would be believable to someone who hasn't heard the current law. Likewise, I'm sure there is more than one way to explain the results scientists have got concerning the laws of gravity. Although, gravity has been tested countless times, giving it a strong case to being correct. BUT, there is always the possibility and always the faith that gravity is the way we think it is.
I'm skeptical of believing everything I hear in Chemistry class. I know my teacher thinks he's teaching us scientific truths, but are they? He hasn't done experiments on a particle level himself to know for certain. He just goes by the book he's given that scientists have brought together. Chemistry is a new science with lots of untruthful information out there. I'm just putting faith that what I learn is correct, whether it's correct or not.