work at something—be busy or occupied with smth.; apply one’s efforts to smth.:
- Is Tom still working at the new book that he promised?
work on something—
1. = work at something:
- I’m presently working on the new book, another suspense novel, after which I plan to write a book for aspiring writers.
2. influence smth.; have an effect on smth.:
- Acebutolol is taken orally so that it works on the central nervous system of those prone to heart attacks.