What is meant by pressure?

• A. The velocity of a moving object.
• B. The heat content of a substance.
• C. The volume of a container.
• D. Force that acts on a unit area.

Answer: (D)

Pressure is the force applied perpendicular to a surface divided by the area over which that force acts. This describes how concentrated a force is on a surface: the same force on a small area yields higher pressure, while the same force on a larger area yields lower pressure. In fluids, pressure comes from particles colliding with surfaces, pushing outward in all directions. That’s why units are pounds per square inch (psi) or pascals (N/m²).

Velocity is speed, not how force is distributed on a surface. Heat content refers to the energy stored in a substance, not the distribution of force. Volume is the amount of space something occupies, not the distribution of force per area.