# Box on an inclined plane

Suppose a box is sitting, motionless, on an inclined plane which makes an angle $\theta$ with the horizontal. If I'm not mistaken, if one writes out Newton's law in the $y$ direction (if $+y$ is up), one gets $N \cos \theta - mg = 0$; i.e., $N = mg \sec \theta$. However, if you ROTATE the coordinate system so that the $x$ axis points along the incline, you get that $N = mg \cos \theta$, which is apparently RIGHT. What's going on here? Why are these two cases different?