Final answer:
The terms firmness, stiffness, or hardness refer to a material's resistance to pressure, abrasion, or deformation. Hardness is rated qualitatively via the Mohs' scale, tensile strength quantitatively measures how much force a material can withstand before deformation, and pressure is the force per unit area applied on a surface.
Step-by-step explanation:
The concept referred to in the question as bristle resistance to pressure, often described in terms of firmness, stiffness, or hardness, is a material or mineral's ability to resist deformation or permanent changes when a force is applied. In the world of physics and material science, this concept is quantitatively described using different measures, such as hardness, tensile strength, and pressure.
Hardness is a specific measure of how resistant a mineral is to abrasion or scratching. The Mohs' scale of mineral hardness classifies minerals according to their relative ability to scratch one another but is not quantitative in that the scale doesn't represent a linear progression of resistance.
Tensile strength refers to the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the sample's cross-section starts to significantly contract. Tensile strength is connected to how a material or object reacts to tensile (stretching or pulling) forces and is an important factor when considering a material for applications that require it to endure such stresses without breaking.
Pressure, in a fluid mechanics context, is the force exerted on a surface per unit area. It is a scalar quantity, meaning it has magnitude but no direction, and is described by the formula P = F/A. Pressure can be felt when submerged in a fluid, such as water, and is experienced as hydrostatic pressure within the human body, as in the case of blood pressure, which is the force exerted by blood against the walls of blood vessels.