Friction is never zero on Earth due to several factors. Here are a few reasons why friction exists and is generally present in most everyday situations:
Surface roughness: Almost all surfaces, even those that appear smooth to the naked eye, have microscopic imperfections and irregularities. When two surfaces come into contact, these irregularities interlock with each other, resulting in friction.
Electrostatic forces: Surfaces can develop electrostatic charges, causing them to attract or repel each other. These forces contribute to friction between objects in contact.
Adhesive forces: Certain materials have adhesive properties, which cause them to stick together when in contact. These adhesive forces contribute to friction and make it difficult to separate the surfaces.
Air resistance: When an object moves through the air, it experiences air resistance, also known as drag. This resistance opposes the motion of the object, creating friction in the process.
Intermolecular forces: Even in the absence of external forces, the molecules of a material are attracted to each other by intermolecular forces. These forces create resistance when an object attempts to slide or move across the surface.
While friction can be reduced or minimized under specific conditions, achieving zero friction is practically challenging. In certain cases, lubrication, smooth surfaces, or low contact forces can significantly reduce friction, but eliminating it entirely is not feasible in most real-world scenarios.