How is pressure defined in physics?

Pressure in physics is defined as the force exerted per unit area. This means that pressure quantifies how much force is distributed over a specific surface area. Mathematically, it is expressed as:

[ \text{Pressure} = \frac{\text{Force}}{\text{Area}} ]

This definition is crucial in various applications, such as fluid mechanics and material science, where understanding how forces interact with surfaces helps explain behaviors of gases and liquids, as well as how structures withstand loads.

In contrast, the other definitions provided do not accurately represent pressure. Energy per unit volume relates to concepts like energy density but does not describe how forces affect areas. The speed of particles in a gas pertains to kinetic theory and temperature but is not a measure of pressure. Similarly, mass of a substance per unit area does not reflect how forces interact with surfaces, although it may suggest density concepts in some contexts. Thus, the definition emphasizing force per area captures the essence of pressure effectively.