Which physical quantity is defined as force per unit area?

• A. Energy
• B. Mass
• C. Pressure
• D. Density

Answer: (C)

Pressure is defined as force per unit area. When a force acts on a surface, the intensity of that contact depends on how much force is applied and how spread out it is over the area. If you push with more force or on a smaller area, the pressure increases; push with the same force on a larger area and the pressure decreases. The standard unit is the pascal, which is one newton per square meter.

In refrigeration and many practical contexts, understanding pressure is essential because it governs how the refrigerant flows and how much load the components must withstand. Energy, mass, and density describe different things: energy is the ability to do work, mass is the amount of matter, and density is mass per unit volume.