I have begun my studies in 'Motion in a straight line', this is a really easy topic, but I don't fully understand this sign thing. I'd firstly like to point out that I understand velocity and acceleration are vector quantities and thus must have a direction associated with it. I've also read that there are different ways to show direction, however, the most common way is either a positive or negative sign before the magnitude of whatever you're calculating.
Velocity, I think, is simple enough. The sign is determined by whether the object has moved in the positive direction or the negative direction. However, deriving the sign for acceleration I find quite tricky and I would like a explanation that makes me understand what it's going.
I really don't want to be given rules, since I can't actually understand what's going by just applying rules.