Rolling friction compared to sliding friction is:

### Understanding Friction Friction is the force that opposes the relative motion between two surfaces in contact. There are two primary types of friction to consider in this context: 1. **Sliding Friction (Kinetic Friction):** This occurs when one surface slides over another. The microscopic irregularities of the two surfaces interlock, requiring a significant force to break these 'cold welds' and maintain motion. 2. **Rolling Friction:** This occurs when a spherical or cylindrical object (like a wheel or ball bearing) rolls over a surface. ### Why Rolling Friction is Smaller In sliding friction, the entire surface area of the object in contact with the ground must overcome interlocking irregularities. In rolling friction, the area of contact is much smaller (theoretically a point or a line), and the 'interlocking' is minimal because the surfaces do not rub against each other significantly. Mathematically, the coefficients of friction are related as follows: $$\mu_r < \mu_k < \mu_s$$ Where: - $\mu_r$ is the coefficient of rolling friction. - $\mu_k$ is the coefficient of sliding (kinetic) friction. - $\mu_s$ is the coefficient of static friction. Because the work done against friction is much lower when rolling, **rolling friction is smaller than sliding friction**.