Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Friction is a force that opposes the relative motion between two surfaces in contact. It acts in a direction opposite to the direction of motion.
Friction is often referred to as a 'Necessary Evil' because while it causes energy loss and wear, it is essential for most daily activities.
Advantages of Friction: It allows us to walk without slipping by providing grip between our feet and the ground. It enables writing on paper as the pen/pencil tip interacts with the surface irregularities. It allows vehicles to stop when brakes are applied and helps in lighting a matchstick through the generation of heat.
Disadvantages of Friction: It causes wear and tear of moving parts, such as the soles of shoes and tires of vehicles. It produces heat, which can damage machinery and sensitive electronic components. It also leads to energy loss as a portion of the applied energy is spent overcoming the frictional force.
Ways to Increase Friction: Increasing surface roughness (e.g., treading of tires, spikes on shoes for athletes) or increasing the normal force () pressing the surfaces together.
Ways to Reduce Friction: Using lubricants like oil or grease, using ball bearings to convert sliding friction into rolling friction, and streamlining the shapes of objects (especially in fluids) to reduce drag.
The magnitude of friction depends on the nature of the surfaces in contact and the force with which the two surfaces are pressed together. It is independent of the area of contact for a given load.
📐Formulae
💡Examples
Problem 1:
Why is it difficult to walk on a wet marble floor or a floor with spilled oil?
Solution:
The presence of water or oil acts as a lubricant, filling the micro-irregularities of the floor surface. This significantly reduces the coefficient of friction ().
Explanation:
Since the frictional force is reduced, the floor cannot provide the necessary reaction force (grip) to push the person forward, causing them to slip.
Problem 2:
Why do the brake pads of a bicycle wear out after some months of use?
Solution:
Brake pads work on the principle of friction. When brakes are applied, the pads press against the rim, creating a high frictional force to stop the motion.
Explanation:
Continuous rubbing between the pads and the rim causes mechanical wear and tear due to the interlocking of surface irregularities, which eventually erodes the material of the pads.
Problem 3:
In many machines, why are ball bearings used between the moving parts?
Solution:
Ball bearings are used to replace sliding friction with rolling friction.
Explanation:
Since the magnitude of rolling friction () is much smaller than sliding friction (), the use of ball bearings reduces energy loss and prevents the machinery from overheating.