Which type of friction occurs when an object slides on a surface?

The type of friction that occurs when an object slides on a surface is indeed sliding friction, sometimes referred to as kinetic friction. This form of friction acts between surfaces that are in relative motion to each other. When an object, such as a block or a piece of furniture, is pushed across a floor, the resistance to its motion is due to the interactions between the surfaces in contact.

Sliding friction is typically lower than static friction, which is the friction that must be overcome to start moving an object that is at rest. Once the object is in motion, sliding friction takes over and influences how easily the object continues to slide. This concept is vital in various applications, such as in machinery and transport systems, where understanding the forces at play can help in optimizing performance and energy efficiency.

The other types of friction listed involve different scenarios: static friction relates to stationary objects, rolling friction pertains to objects that roll over a surface (like wheels), and fluid friction involves objects moving through a fluid (liquid or gas). Each of these types of friction has its characteristics based on the nature of the movement and the surfaces involved.