Definition of Rolling Friction
Rolling friction, also known as rolling resistance, is the force that resists the motion when a body rolls over a surface. Unlike sliding friction, which opposes direct sliding contact, rolling friction arises from the deformation of the rolling object, the surface it rolls on, or both, as they come into contact.
Causes and Characteristics
The primary cause of rolling friction is the temporary deformation of the materials involved. As a wheel or ball rolls, it slightly deforms the surface ahead of it, creating a small 'hill' that the rolling object must continuously climb. Additionally, the rolling object itself may deform. Energy is dissipated as heat during these deformations, leading to resistance. It is generally much weaker than sliding friction for hard, non-deforming surfaces.
Practical Examples
A classic example of rolling friction is a bicycle wheel moving across pavement. The tire slightly flattens where it meets the road, and the road surface itself might subtly indent. As the wheel rotates, the tire must constantly 'climb out' of this slight depression, and the road surface must recover its shape, causing resistance. Similarly, a ball rolling on a soft carpet experiences significant rolling friction due to the carpet's deformation.
Importance and Applications
Understanding rolling friction is critical in many engineering and design applications. Minimizing rolling resistance is vital for improving fuel efficiency in vehicles (tires are designed to reduce it) and for the smooth operation of machinery (ball bearings convert sliding motion to rolling motion to reduce friction and wear). Conversely, in some cases like traction, a certain amount of rolling friction is desired for grip.