Today I came in class and in one of the problems the teacher used $\vec{a}=\vec{\omega}\times \vec{r}$ which made me very confused because I don't know where it comes from, it seems pulled out of thin air, the only one I know of is $\vec{v}=\vec{\omega}\times \vec{r}$ which then as well confuses me more since that would imply that acceleration and velocity are the same and that's not true. What's going on here?