Vectors are usually the first thing you learn in a physics class, and they’re the first thing you’ll learn here. Vectors are one of the fundamental mathematical tools the physicist uses, and one that is frequently misunderstood or misapplied by students. Generally, there aren’t more than one or two questions on SAT II Physics that test your knowledge of vectors directly, but there are a host of problems—particularly in mechanics—where arriving at the right solution demands a solid grasp of how to apply and manipulate vectors. Even if you feel confident with vectors, we urge you to review this chapter and be absolutely sure you won’t get tripped up on what would otherwise be some easy questions.