Friction basics — angle of friction The angle which the normal reaction makes with the resultant reaction between two contacting surfaces is called the angle of friction. Do you agree?

Introduction / Context:
The angle of friction is a key geometric way to visualize the frictional interaction between two surfaces. It links the friction coefficient to the orientation of the resultant reaction force.

Given Data / Assumptions:

• Contact between two rigid bodies with dry (Coulomb) friction.
• Normal reaction N and limiting friction F_max = μ N define the resultant reaction R.
• Angle of friction φ is defined at the threshold of sliding (impending motion).

Concept / Approach:
At limiting equilibrium, the resultant reaction R is the vector sum of N and F_max. The angle φ between R and N satisfies tan(φ) = F_max / N = μ. Thus, φ is literally the angle that the normal makes with the resultant reaction, consistent with the statement.

Step-by-Step Solution:

Verification / Alternative check:
If μ = 0 (perfectly smooth), φ = 0 and R aligns with N—consistent. Larger μ leads to larger φ, again matching intuition.

Why Other Options Are Wrong:

• Disagree / conditional agreements: The definition does not require smoothness or kinetic sliding; it is defined at the limiting state for static friction.

Common Pitfalls:
Confusing angle of friction φ with angle of repose (inclination of an incline at impending slip). They are equal in magnitude but represent different geometric contexts.

Final Answer:
Agree