Here's why:
* Curv is the base form of the word, and it signifies "bending" or "having a curve."
* Curved is formed by adding the past participle suffix "-ed" to the root word.
Other words that share the same root include:
* Curvature (the state of being curved)
* Curvilinear (having a curved line)
* Cursive (writing in flowing, connected strokes)