AIIMS 2006 Physics Friction Assertion Reason Question

Explanation of the Question

In the given question, we have two statements: the Assertion and the Reason. Let’s analyze each of them in detail.

Assertion: "Use of ball bearings between two moving parts of a machine is a common practice."
This statement is true. Ball bearings are widely used in machinery to facilitate smooth movement between parts that rotate or move relative to each other. The primary function of ball bearings is to reduce friction between the moving parts, which is essential for the efficient operation of machines.

Reason: "Ball bearings reduce vibrations and provide good stability."
This statement is false in the context provided. While ball bearings do reduce friction and can help in minimizing certain types of vibrations, they do not inherently provide stability in the sense of preventing all types of vibrations. Stability and vibration damping often require additional design considerations such as the geometry of the components, the materials used, and the overall design of the assembly.

Why the Correct Answer is C

The correct answer is C: "Assertion is true but Reason is false."

• The Assertion about the common practice of using ball bearings is indeed true because ball bearings are essential in minimizing friction in rotating systems, which is a fundamental principle in mechanics.
• The Reason, however, is misleading as it implies that ball bearings universally reduce all vibrations and provide stability, which is not entirely accurate. They may reduce friction-induced vibrations, but they do not guarantee stability across all operating conditions.

Clarification of Other Options

• Option A: "Both Assertion and Reason are true and Reason is the correct explanation of Assertion."
  Incorrect because while the Assertion is true, the Reason is false. Thus, the Reason cannot be a correct explanation of the Assertion.

• Option B: "Both Assertion and Reason are true but Reason is not the correct explanation of Assertion."
  Incorrect because the Reason is not true at all. Therefore, this option misrepresents the truth of the statements.

• Option D: "Both Assertion and Reason are false."
  Incorrect because the Assertion is true. Therefore, this option cannot be correct.

Relevant Concepts

1. Friction and Bearings:
   Ball bearings are used primarily to reduce friction between moving parts. The friction force can be described by the formula:

   $F_f = \mu N$

   where $F_f$ is the frictional force, $\mu$ is the coefficient of friction, and $N$ is the normal force. By utilizing ball bearings, the effective value of $\mu$ can be minimized, significantly decreasing the frictional force acting on moving parts.

2. Rotational Mechanics:
   In machines where rotation is a key factor, ball bearings allow for smoother operation, reducing wear and increasing efficiency. The principle of rotational motion involves concepts such as angular velocity and torque, which are essential for understanding how ball bearings function within a machine.

In summary, the Assertion is true as ball bearings are indeed a common practice in machinery to reduce friction. However, the Reason is false because ball bearings do not universally provide stability or reduce all vibrations. Thus, the correct answer is C.