Useful friction refers to the frictional force that serves a beneficial purpose in a particular context. Here are examples of high useful friction and low useful friction:
High useful friction:
Traction between car tires and the road: When driving, the friction between the tires and the road surface provides the necessary traction for the vehicle to accelerate, decelerate, and maneuver safely. Adequate friction allows the tires to grip the road effectively, preventing skidding or sliding.
Shoe grip on the ground: Friction between the soles of shoes and the ground provides necessary traction, allowing us to walk, run, and maintain balance. Shoes with high friction soles are especially useful in sports like basketball or tennis, where quick changes in direction require good grip.
Brakes in vehicles: Friction between the brake pads and the brake rotors/discs generates the necessary resistance to slow down or stop a vehicle. The high friction converts the kinetic energy of the moving vehicle into heat, effectively reducing its speed.
Low useful friction:
Reducing air resistance: In certain situations, such as in aerodynamics or during the design of high-speed vehicles like airplanes or cars, minimizing air resistance (also called drag) is desirable. Streamlined shapes and smooth surfaces are designed to reduce the friction between the moving object and the surrounding air, allowing it to move more efficiently.
Lubrication: In mechanical systems, the use of lubricants like oil or grease reduces friction between moving parts, minimizing wear and tear. By providing a thin film between surfaces, lubricants allow smooth movement, reducing the amount of friction and energy loss.
Ice skating: Ice has very low friction, allowing ice skaters to glide smoothly across the surface. The low friction between the skates and the ice minimizes resistance, enabling skaters to achieve high speeds and perform intricate maneuvers.
In both cases, whether high or low useful friction, the specific context and requirements determine whether the friction is considered beneficial or undesirable.