How to find a normal vector in 2D I hope this is not a stupid question.  I am having a hard time finding a normal in 2D.  I am working on a game project and I am trying to perform vector reflection during collision.  I know the rest of the math, but I am having a hard time creating the normal vector that is required.
Is there a way to build a normal vector from the point of collision?  What do I need to create the normal vector?  My position vector does not necessarily point in the direction of the object.  My position can be (100, 200) but the object is a vertical object for example.  What else can I do for this?
$\vec V_{reflected} =\vec V_{incident} -2\vec n(\vec V_{incident} \cdot \vec n)$
I also had this problem. you can do $\vec{v} \times \vec{p}$ and consider $x$ and $y$ coordinates only. 

In fact for any $\vec{v}=(x,y,0)$ and $\vec{p}=(0,0,1)$ then $\vec{v} \times \vec{p}=\begin{bmatrix}\vec{i} &amp; \vec{j} &amp; \vec{k}\\x &amp; y &amp; z \\ 0 &amp; 0 &amp; 1\end{bmatrix} = y\vec{i}-x\vec{j}+0\vec{k}=(y,-x)$

That implies that the normal vector $\vec{n}=(\vec{V}y, -\vec{V}x)$