Main differences between physicists and engineers?

Physicists are generally concerned with learning how the universe operates. They're not necessarily concerned with practical applications of that knowledge. The physicists I know use engineering to build apparatuses and perform experiments (I know a low-temperature physicist who, when people ask what he does for a living, says "oh, I'm a plumber," because a lot of his job involves designing and building gizmos with lots of complicated plumbing for liquid helium), but at the end of the day their goal is not to build things. That's a means to an end. They're after knowledge.

Engineers are generally concerned with designing and/or making things that work. The engineers I know use a knowledge of physics to do so, but at the end of the day, their goal is not to probe the rules by which the universe operates. Knowledge of physics is a means to an end. They're after creating something that works.