Determine the normal between two objects

You mention pixels, so I'm assuming these are sprites in a 2d context. This is IMO, but I think you'd have better luck representing your objects with geometric primitives for the purpose of collision detection and response. The problems you're trying to solve - finding a normal and point of collision, reflecting the velocity, etc. - all have established solutions in geometrical terms. Circles, for example, are very easy to work with.

Also, in a 2d game environment it's best not to think of lines in terms of slope (even though that's the way we learn about them in beginning algebra). That representation isn't particularly useful for 2d simulations; the vector form is to be preferred.

The problem you describe has been discussed ad infinitum on these boards, but with the search function disabled the threads may be hard to find. If you're interested in the geometric (rather than sprite-based) solution, though, I'm sure someone would be glad to explain the basics to you.

I'm not completely sure what you're asking for, but it seems like vector reflection might be it.

(Look at the bottom diagram on that link.)

Thanks for the replies, esp. whoever is "Anonymous"...that is exactly what kind of info I was looking for!! Thank you!!!