Pressure Defined as Force per Unit Area

Steps:

• Recall the standard definition of pressure in physics: it measures how force is distributed over a surface.
• Identify the formula: pressure equals force divided by the area over which it acts (P = F/A).
• Compare choices to the formula: option A matches exactly as force per unit area.
• Eliminate mismatches: B, C, and D involve mass or weight over area/volume, not force.

Why A is correct:

• Pressure is defined by the formula P = F/A, where force (F) is applied per unit area (A), as per Newton's laws and fluid mechanics.

Why the others are wrong:

• B describes surface mass density, not pressure.
• C defines mass density (ρ = m/V), unrelated to force.
• D represents specific weight (γ = weight/volume), which is density times gravity, not pressure.

Final answer: A