The "first law" often refers to Newton's First Law of Motion, which states that an object at rest will remain at rest, and an object in motion will continue in motion at a constant velocity unless acted upon by a net external force. This principle highlights the concept of inertia, which is the tendency of objects to resist changes in their state of motion. In practical terms, this means that if you slide a book across a table, it will eventually stop due to the friction between the book and the table. Similarly, a ball thrown in space will keep moving indefinitely unless it encounters another force, such as gravity or air resistance.