Multiple Choice
In the context of kinetic friction in machinery, how do ball bearings primarily reduce friction compared with two surfaces sliding directly against each other?
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7. Friction, Inclines, Systems
Kinetic Friction
Multiple Choice
In the context of kinetic friction between two solid surfaces, which method will most directly reduce the kinetic frictional force for a given normal force ?
A
Apply a lubricant between the surfaces to reduce the coefficient of kinetic friction .
B
Increase the normal force by pressing the surfaces together more strongly.
C
Increase the contact area while keeping the materials and normal force the same.
D
Increase the roughness of both surfaces to increase mechanical interlocking.
Verified step by step guidance1
Recall the formula for kinetic frictional force: \(f_{k} = \mu_{k} N\), where \(f_{k}\) is the kinetic frictional force, \(\mu_{k}\) is the coefficient of kinetic friction, and \(N\) is the normal force.
Understand that for a given normal force \(N\), the kinetic frictional force \(f_{k}\) depends directly on the coefficient of kinetic friction \(\mu_{k}\).
Analyze how each method affects \(\mu_{k}\) or \(N\): applying a lubricant reduces \(\mu_{k}\), increasing normal force \(N\) increases \(f_{k}\), increasing contact area does not affect \(f_{k}\) significantly in kinetic friction, and increasing roughness tends to increase \(\mu_{k}\).
Conclude that the most direct way to reduce \(f_{k}\) for a fixed \(N\) is to reduce \(\mu_{k}\) by applying a lubricant between the surfaces.
Therefore, applying a lubricant lowers the coefficient of kinetic friction, which directly reduces the kinetic frictional force without changing the normal force.
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