NCEA Level 2 Physics Practice Exam 2026 - Free Physics Practice Questions and Study Guide

According to Newton's First Law of Motion, often referred to as the principle of inertia, if no net force acts on an object, it will either remain at rest or continue to move in a straight line at a constant speed. This means that an object in motion does not require a force to keep moving; instead, it only requires a force to change its state of motion. This law essentially states that an object's velocity will remain constant unless acted upon by an external net force.

Therefore, if an object is at rest, it will stay at rest, and if it is in motion, it will maintain its velocity (which includes both speed and direction) until a net external force causes a change. This understanding of inertia is fundamental in analyzing motion and the effects of forces in a variety of physical situations.