Non-conservative forces are dissipative forces such as friction or air resistance. These forces take energy away from a system as it progresses. Unlike conservative forces, non-conservative forces do not have potential energy associated with them. This is because the energy is lost to the system and cannot be turned into useful work later.

Also unlike their conservative counterparts, they are path-dependent; where the object starts and stops does matter. For example, a grinding wheel applies a non-conservative force because the work done depends on how many rotations the wheel makes. In addition, a non-conservative force turns a macroscopic movement into a microscopic movement. For example, when a ball hits a bat, it creates a sound, which is a microscopic motion. Also, the shape of the ball is momentarily deformed due to the collision with the bat; when the ball bounces from the bat, it returns to its original shape. Throughout all of this, the atoms of the ball, bat, and the atmosphere will experience vibration and lose some of their energy in the form of heat.

This text is adapted from Openstax, University Physics Volume 1, Section 8.2: Conservative and Non-Conservative Forces.