Question

If the coefficient of friction between brake lining and drum decreases, the braking effort required

• A. Increases
• B. Decreases
• C. Remains constant
• D. Becomes zero

Hint:

A decrease in friction coefficient is also known as "brake fade".
To maintain the same stopping distance under brake fade conditions, the driver has to push the brake pedal much harder (higher braking effort).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question focuses on the operational performance of mechanical brakes.
We need to determine how a reduction in the coefficient of friction ($\mu$) between the brake lining and drum affects the required braking effort (applied force).

Step 2: Key Formula or Approach:
The braking torque ($T_b$) developed by a brake is directly proportional to the normal force ($R_N$) and the coefficient of friction ($\mu$):
\[ T_b = \mu \cdot R_N \cdot r \]
where $r$ is the radius of the brake drum.
The braking effort (actuating force $P$) applied to the lever is directly related to the normal reaction force $R_N$ through the geometry of the lever.

Step 3: Detailed Explanation:

• To stop a vehicle or rotating component, a specific braking torque ($T_b$) is necessary to overcome the kinetic energy.

• From the braking torque equation, we have:
\[ R_N = \frac{T_b}{\mu \cdot r} \]

• If the coefficient of friction $\mu$ decreases (due to wear, heating, oil contamination, etc.), the normal force $R_N$ required to generate the same level of braking torque must increase.

• Since the actuating effort ($P$) is proportional to $R_N$, the required braking effort must increase to compensate for the lower friction.

Step 4: Final Answer:
If the coefficient of friction decreases, the braking effort required increases.