Physics are often really difficult to understand or even believe when you're first learning them. In one of my classes we did an experiment where you have two balls on some springy thingy. What happens is that one ball drops straight down and the other is given an initial horizontal velocity by the spring. Since they're launched from the same height and neither have and initial vertical velocity, they land at the same time. My teacher didn't plan on doing the experiment, but when we went over a problem in class that brought up a similar idea, we all had such a terrible time believing that it was possible that both balls would land at the same time. The classic gravity experiment with a rock and a feather is similar. When you neglect air resistance, they both will land at the same time when dropped. Thats a tough one to swallow when you first learn it. And it seems there's a lot of things like that in physics. My question is why is that? Is it something we're taught as kids that makes it hard for us to believe these things later on? Is it some human nature thing? It seems just about everyone has a hard time with these sort of concepts. Reason?