What would happen to an object in motion without any external forces acting on it?

An object in motion, when not influenced by any external forces, will continue to move in a straight line at a constant speed. This principle is rooted in Newton's first law of motion, often referred to as the law of inertia. Inertia is the property of matter that causes it to resist changes in its state of motion. Therefore, unless an external force like friction, gravity, or another kind of force acts upon it, the object will not change its motion and will persist in its current state. This is why the concept of inertia is fundamental in understanding motion and forces in physics.