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Difficulty: EasyFriction and Resistance

A heavy rectangular crate is being dragged across a level warehouse floor. If the crate is stopped, flipped to rest on its narrowest side, and then dragged again, how will the force of sliding friction change?

  1. It remains the same.Answer
  2. B
    It decreases because there is less surface area touching the floor.
  3. C
    It increases because the crate's weight is concentrated into a smaller area.
  4. D
    It changes because the crate's inertia is altered by its new position.

Answer

The force of sliding friction remains the same.
The correct answer states that friction remains the same. According to the laws of classical physics, sliding (kinetic) friction is determined by multiplying the normal force (the weight of the crate) by the coefficient of friction (the material properties of the floor and crate). Because flipping the crate changes neither its overall weight nor the materials involved, the total frictional resistance remains unchanged.

Step-by-Step Solution

1
Identify the factors that determine sliding friction.
Sliding friction relies on the normal force (the crate's weight) and the coefficient of friction (the roughness of the floor and crate materials).
These are the only physical variables present in the standard friction formula (F=μNF = \mu N).
2
Evaluate what changes when the crate is flipped.
The surface area touching the floor decreases, but the crate's mass, weight, and material remain exactly the same.
Flipping an object only changes its orientation, not its inherent properties.
3
Determine the impact of contact area on friction.
The frictional force does not change.
Because neither the normal force nor the surface materials have changed, the total resistance remains constant regardless of the contact area size.

Key Concept

Sliding friction depends only on the normal force and the coefficient of friction between the two surfaces, and is independent of the apparent area of contact.
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Topics

Friction and Resistance

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