Match each mechanical adjustment to its primary physical effect on frictional resistance.
- Introducing motor oil between two dry, sliding metal platesDecreases the coefficient of friction by separating the solid surfaces
- Adding heavier cargo to a pallet being dragged across a level floorIncreases the normal force, resulting in higher total frictional resistance
- Installing ball bearings between a rotating axle and its housingReplaces sliding friction with rolling friction, reducing overall resistance
- Turning a sliding rectangular crate so it rests on its largest face instead of its smallest faceLeaves the total frictional resistance unchanged, as friction is independent of contact area
Answer
Motor oil decreases the coefficient of friction; adding cargo increases the normal force; ball bearings replace sliding friction with rolling friction; and changing the resting face of a crate leaves the frictional resistance unchanged.
Each adjustment demonstrates a fundamental principle of friction. Oil modifies the surface interaction (lowering the coefficient of friction). Added mass increases the normal force (increasing total resistance). Bearings change the physical mechanism from sliding to rolling. Finally, rotating the crate tests the principle that friction is independent of the contact area.
Step-by-Step Solution
Key Concept
Friction and Resistance