Stress is a measure of internal force per unit area. Which of the following expresses valid SI-consistent units for stress?

Introduction / Context:
Stress (σ or τ) quantifies internal forces distributed over a cross-sectional area. Its SI unit is the Pascal, defined as 1 N/m^2, but engineering practice commonly uses scaled units such as N/mm^2 or N/cm^2 for convenience with typical magnitudes.

Given Data / Assumptions:

• Stress = Force / Area.
• Force unit: Newton (N).
• Area units: m^2, cm^2, mm^2 are all valid metric areas.

Concept / Approach:
Any combination of Newtons divided by a squared length unit yields a pressure/stress unit. Conversions are straightforward: 1 N/mm^2 = 10^6 N/m^2 (MPa), and 1 N/cm^2 = 10^4 N/m^2 (0.1 MPa). Therefore, N/m^2, N/cm^2, and N/mm^2 are all valid stress units; the Pascal is the SI base (N/m^2).

Step-by-Step Solution:
Write the definition: stress = force / area.Identify SI base: N/m^2 = Pa.Acknowledge engineering scales: N/mm^2 (MPa) and N/cm^2 (0.1 MPa).Therefore, all listed unit forms are acceptable expressions of stress.

Verification / Alternative check:
Perform conversions: 1 N/mm^2 = (1 N)/(10^-6 m^2) = 10^6 N/m^2.1 N/cm^2 = (1 N)/(10^-4 m^2) = 10^4 N/m^2.Consistency confirms validity.

Why Other Options Are Wrong:

• None of these: Incorrect because all three are legitimate unit expressions.

Common Pitfalls:
Believing only N/m^2 is correct; confusing kgf/cm^2 with N/cm^2; mixing mass and force units.

Final Answer:
All of the above (unit-consistent pressure measures)