One of the most basic concepts related to force and motion is Newton's first law, which essentially states, "An object at rest tends to remain at rest unless acted on by an unbalanced force. An object in motion in a straight line tends to remain in motion in a straight line unless acted upon by an unbalanced force." Judging by the time and space devoted to this law (usually a paragraph and at most a page in a book) in most curricula, one would think the law is just plain obvious and does not require much investigation. But is this law of motion really that obvious? The authors decided to find out how obvious Newton's first law was to students of different ages and to see how well these students would respond to activities constructed to help them understand the law. They took a set of inquiry activities designed to help adults understand the reasoning behind Newton's first law and adapted them for a third-grade classroom and a sixth-grade classroom. In this article the authors present the general procedures they used and discuss their results for the different grade levels.