What is the resistance to movement between two masses in contact with each other called?

The term that describes the resistance to movement between two masses in contact with each other is friction. Friction occurs when two surfaces interact and can impede or slow down motion. It plays a crucial role in various applications, including braking systems in vehicles, where friction is necessary to stop the wheels from turning.

Friction arises due to the microscopic interactions between the surfaces of the two objects and is influenced by several factors, such as the types of materials, the roughness of the surfaces, and the force pressing them together. This makes friction a fundamental concept in physics and engineering, particularly in systems where movement and resistance are crucial, such as in the functionality of brakes.

The other terms refer to different concepts: inertia pertains to the property of an object to resist changes to its state of motion, drag refers to the resistance experienced by an object moving through a fluid (like air or water), and pressure typically relates to force exerted per unit area and does not specifically reference the resistance between two solid bodies. Understanding these distinctions helps clarify the specific context where friction is applicable.