How can I draw a perfect parabola on my computer?

I'm trying to write up homework solutions in MS Word, for a physics class. I know how to draw something that approximates a parabola using the curve tool, but I'd rather have a real parabola. Is there a way to do that, where I can get just the line (I don't want a graph, I'm using a parabola in a diagram showing the motion of a projectile)? I have the full MS Office suite (2010), and Photoshop (plus a bunch of other Adobe products).

What I usually do is draw my diagrams free-hand and scan them in, or I just use the curve tool and not worry about it being perfect. But since it's such a basic shape (in physics, at least) I thought there really should be a better way. Same goes for ellipses, especially when I teach astronomy!