Question

Frictional force of granular material is -

(A) Proportional to normal load

(B) Independent of the area of the sliding surface

(C) Proportional to actual area of contact

(D) Dependent on nature of material in contact

Choose the correct answer from the options given below:

• A. (A) and (C) only
• B. (A), (B), (C) and (D)
• C. (A), (B) and (D) only
• D. (C) and (D) only

Hint:

Recall the three classical laws of friction taught for sliding solids and check each statement against them.

Answer 1

The Correct Option is C

Step 1: Friction between granular agricultural materials and a surface is generally explained through the same classical laws of friction taught for solids sliding on surfaces.

Step 2: The first law says frictional force is directly proportional to the normal load pressing the surfaces together, F = mu x N. This matches statement (A), which is correct.

Step 3: The second law says frictional force is independent of the apparent area of the sliding surface, doubling the nominal contact area without changing the load does not change the friction force. This matches statement (B), which is correct.

Step 4: The third law says frictional force depends on the nature of the two surfaces in contact, their roughness, moisture content, and material type all affect the coefficient of friction mu. This matches statement (D), which is correct.

Step 5: Statement (C), proportional to the actual area of contact, goes against the second classical law, since that law explicitly states friction does not scale with contact area. So (C) is not part of the standard laws used here and is incorrect.

Step 6: Only (A), (B) and (D) hold, so option 3 is correct.