Is this science or a sort of engineering? How do I learn more about it?

sounds like you're a Maker. Check into Makerfaire's, maker spaces, Make magazine, etc. http://en.wikipedia.org/wiki/Maker_culture

Try http://en.wikipedia.org/wiki/Aquaculture: critters and tanks and 'hands on' definite check.

Civil engineering?

I am not a scientist or engineer, but I do classify jobs in those fields. Your interests sound like engineering to me. Some specific fields that come to mind are mechanical, environmental and agricultural engineering. Have you checked out the MIT open course offerings? That might be a good place to start.

ITEC/Industrial Engineering.

You say computers and programming are not your thing, but I think you would enjoy an Arduino. It fits with your desire to learn about robotics. The programming environment is relatively simple, and I think once you start controlling the world around you instead of numbers in a computer you will be hooked. Check out controlling solenoid valves and relays with an Arduino to get an idea of what I am talking about. You might enjoy a book on fluid mechanics at the library. I wouldn't spend a ton of money on a textbook. I think the knowledge contained in a fluid mechanics book will be beyond what you care to know about for what you are doing, but you never know what you will glean from a resource. A book is also going to assume a lot of previous engineering/physics knowledge. Pressure head is a concept from fluid mechanics that you might be interested in though, and you might google the term for the basics. As far as engines and mopeds, small engine repair is a thriving hobby. I know my local community college has a class on small engine repair, and yours might too. Beyond a formal class, I find internet forums to be a great place to learn about stuff like that. There will be quite a few for various types of small engines. You will likely find an entire forum dedicated to putting engines on bicycles.

...hate following directions. So computers and programming aren't really my bag Programming isn't really about following directions. (Well, not for the person doing it!) Sure, it's possible to learn about it by following directions, but that's true of a lot of things. People have written up directions for how to do some of the things you are interested in. Even if you don't want to follow directions it might be helpful to read about how other people have built the things you want to build.

Thanks for your help so far! Just wanted to make a couple clarifications: Programming isn't really about following directions. (Well, not for the person doing it anyhow!) Sure, it's possible to learn about it by following directions, but that's true of a lot of things. People have written up directions for how to do some of the things you are interested in. Even if you don't want to follow directions it might be helpful to read about how other people have built the things you want to build. Sorry, didn't mean to lump programming in with following directions -- I meant programming isn't really my thing because I like to work with my hands and build physical things/manipulate physical stuff. I also like a lot of messiness -- both in terms having to juggle a ton of variables at once and in terms of literal dirt. I enjoyed CodeAcademy OK and Arduino sounds incredibly fun, though, so I should probably give it another go. My thing with following directions is that doing things in a predetermined way takes the fun out of the process for me. That's why I'm not big on kits and thought most science class labs were PITAs. I like reading about how other people have done things, but I want to be able to tweak the process and see what happens for myself. That's why it's important to me to know the theories behind why/how something works, and not just whether it works or not -- so I've got some room to start tweaking it. I also love troubleshooting and looking for ways that models fail, which doesn't exactly endear me to people like my statistics professors and makes it tough for me to sit down and recreate another person's method to a T (even if their method really would be the best way to go). I've looked into MOOCs, but I think I might have to fill a lot of gen.ed. gaps before I can tackle the courses about the specific stuff I'm interested in. I'm open to doing that -- I plan to work through a couple of possibly relevant gen.ed. courses this summer anyway (Calc I & II in particular, for reasons related to my masters program), but that makes MOOCs a pretty long-term solution. Forums (and other online resources) and library books are fantastic, and they've been my bread and butter so far. The problem with them is, though, you can't impose a whole lot of rigor on yourself when you're just futzing around with things on your own. To be honest, at this point, I'm sick of doing everything so intuitively. I'd like to be able to back up what I'm doing with *some* formal skill and knowledge in how to plan/build/assess projects. I get that it takes a long, long time to build that kind of knowledge, and this is basically just for fun anyway, so the stakes aren't high -- but right now I'm sort of at a loss as to what sorts of projects would be good learning experiences for me or even what kinds of fields it might be cool to learn more about. Most of the stuff I can find is either geared to young kids or professionals. If it tells you anything about my interests -- when I was a kid, my "dream job" was to become a construction worker and my favorite field trip of all time was to a trash-powered electric plant. Right now, I'm in grad school for public policy, though.

You'll want something near you, try this map: http://themakermap.com/