Newton's first law, also known as the law of inertia, is a fundamental principle of physics. It states that an object at rest will remain at rest, while an object in motion will continue to move at a constant velocity, unless acted upon by an external force. Synonyms for this law include the law of motion, the principle of inertia, and the first law of thermodynamics. These different terms are often used interchangeably, depending on the context in which they are being discussed. Regardless of the terminology used, Newton's first law provides a crucial foundation for understanding the behavior of objects in motion, and is essential for a wide range of scientific applications.