A heavy steel crate must be moved across a horizontal concrete floor. Rank the following conditions based on the magnitude of frictional resistance opposing the applied force, from LEAST resistance to GREATEST resistance.
- 1Placing the crate on a cart with well-lubricated wheel bearings
- 2Sliding the crate across the floor after coating the surface with a thick layer of oil
- 3Sliding the crate across the dry, clean floor at a constant speed
- 4Pushing the stationary crate on the dry, clean floor just before it breaks free and begins to move
Answer
The correct sequence from least to greatest frictional resistance is: using wheels (rolling friction), sliding on oil (fluid friction), sliding at a constant speed (kinetic friction), and pushing just prior to movement (static friction).
Frictional resistance follows a predictable hierarchy based on how surfaces interact. Rolling friction is the lowest because there is no sliding action. Fluid friction is next, as the fluid layer prevents solid-to-solid contact. Dry kinetic (sliding) friction is higher because the solids scrape directly against each other. Finally, static friction is the highest because the microscopic peaks and valleys of the stationary surfaces have settled deeply into one another.
Step-by-Step Solution
Key Concept
Types of Friction (Static, Kinetic, Rolling, Fluid)