Friction: Test Your Understanding (con't)
Teacher's Guide
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ward
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science
Critical Thinking: Describe what might be happening when a door emits a high-pitched "squeaking"
noise when opened. What are some possible solutions to stop this noise?
Sample answer: Harmonic frictional oscillation caused by a lack of lubrication likely causes the
high-pitched noise. Solutions to this problem include adding more lubrication to the door hinges,
reducing the normal load, increasing the sliding speed, introducing damping into the system, stiffening
all components acting as springs, or changing the hinge materials.
Critical Thinking: Describe what is happening, in terms of normal force, limiting value, and coefficient of
friction, when an individual pushes a heavy box across a carpet as compared to pushing a light box across
the same floor.
Sample answer: When a person pushes a heavy box across the carpet, there is a higher limiting value
because the normal force is greater; therefore, there is a greater coefficient of friction. The individual
needs to apply more force to push the heavier box across the carpet in order to overcome the increased
normal force.
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