When no forces act on a moving object, it will continue to move in a straight line at a constant speed. This is due to the concept of inertia, one of Newton's Laws of Motion.

Here's a breakdown:

* Inertia: This is the natural tendency of an object to resist changes in its motion. An object at rest wants to stay at rest, and an object in motion wants to stay in motion.

* No Forces: If no external forces are acting on the object, there's nothing to change its state of motion.

* Straight Line and Constant Speed: This means the object will travel in a straight path and maintain the same velocity.

Example: Imagine a hockey puck sliding across a frictionless surface. Once it's given an initial push, it will continue to glide in a straight line at a constant speed because there's no friction to slow it down or other forces to change its direction.