What describes the force per unit area applied perpendicular to a surface?

• A. Molecular Weight
• B. Specific Gravity
• C. Vapor Pressure
• D. Pressure

Answer: (D)

Pressure describes the force per unit area exerted on or against a surface in a direction normal to that surface. It’s the concept captured by P = F/A, with common units like psi or kPa. In hazmat scenarios, understanding pressure helps assess how a container will respond to internal forces, including venting or potential rupture, based on the force distributed over the container’s area. The other terms refer to different properties: molecular weight is the mass of a molecule, specific gravity is a density comparison to water, and vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature.