What concept explains that objects at rest will remain at rest unless acted upon?

The principle that states that objects at rest will remain at rest unless acted upon by an external force is known as Newton's First Law of Motion. This law, also referred to as the law of inertia, describes the tendency of objects to maintain their state of motion. Inertia is the property of matter that causes it to resist changes to its state of motion. Therefore, an object that is stationary will not start moving unless a force is applied to it, and an object in motion will continue to move at a constant velocity unless influenced by an external force.

Understanding this law is fundamental to concepts in mechanics, as it establishes a baseline for analyzing motion and the effects of force. It highlights the inherent properties of objects and the need for an external influence to change those properties, which is crucial for predicting the behavior of physical systems.