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Difficulty: MediumFriction and Resistance

A rubber drive belt is slipping on a steel motor pulley because there is insufficient frictional resistance between the two surfaces. Which of the following adjustments will most effectively increase the frictional force to prevent the belt from slipping?

  1. A
    Using a narrower belt to decrease the contact area
  2. Increasing the tension on the drive beltAnswer
  3. C
    Replacing the pulley with a heavier one of the same size
  4. D
    Applying a sudden rotational force to use the pulley's inertia

Answer

Increasing the tension on the drive belt
The correct adjustment increases the belt's tension. Friction depends on two main factors: the materials involved (coefficient of friction) and how hard they are pressed together (normal force). In a mechanical drive system, increasing the belt tension pulls the belt tighter around the pulley, directly increasing the normal force pressing inward. This higher normal force generates a proportionally higher static friction, giving the belt better grip to prevent slipping.

Step-by-Step Solution

1
Identify the formula and components of mechanical friction.
The maximum static frictional force is determined by the equation Ff=μFNF_f = \mu F_N, where μ\mu is the coefficient of friction and FNF_N is the normal force.
Understanding the mathematical relationship reveals which physical variables can be manipulated to change the friction.
2
Determine how normal force is generated in a belt and pulley system.
The normal force (the force pressing the belt perpendicularly into the face of the pulley) is generated by the tension pulling on the ends of the belt.
To increase FNF_N (and thereby increase FfF_f), we must increase the force that squeezes the two components together.
3
Evaluate the given modifications.
Increasing the tension directly increases the normal force. Changing the surface area or pulley mass does not affect the normal force between the mating surfaces.
This confirms that tightening the belt is the mechanically correct method to stop slipping.

Key Concept

Frictional force is directly proportional to the normal force pressing two surfaces together, and in a belt-drive system, this normal force is created by belt tension.
Estimated Time:1m 0s
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Topics

Friction and Resistance

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