| Pin support: | (english) In two dimensions, a pin support restrains two translation degrees of freedom but does not restrain rotation. When considering reaction forces, a pin support is usually considered to have two force components: one each about the x and y axes respectively. |
| Potential Energy: | (english) The energy stored in a raised object (e.g. the weights in a grandfather clock). Potential energy equals mgh, where m is mass, g is the acceleration of gravity, and h is the vertical distance from a reference location. It is called potential energy because the energy can be regained when the object is lowered. This type of potential energy is sometimes called gravitational potential energy in order to distinguish it from elastic potential energy: see elastic energy. |
| Pressure: | (english) Pressure is a similar idea to stress, the force intensity at a point, except that pressure means something acting on the surface of an object rather than within the material of the object. When discussing the pressure within a fluid, the meaning is equivalent to stress. |
| Pathogenic organism | (Environmental Engineering) An organism capable of causing infection. |
| Phenol | (Environmental Engineering) An aromatic benzene ring with a hydroxyl substituted for one hydrogen. |
| Phenyl- | (Environmental Engineering) A benzene ring named as a constituent group, C6H5-. |
| Phosphorylation | (Environmental Engineering) The synthesis of the energy storage compound adenosine triphosphate (ATP) from adenosine diphosphate (ADP). |
| Photoautotrophic | (Environmental Engineering) Organisms which utilize inorganic carbon dioxide for protoplasm synthesis and light for an energy source. See autotrophic and chemoautotrophic. |
| Photochemical pollutants | (Environmental Engineering) Chemicals which react photochemically (in the presence of sunlight) to destroy ozone in the stratosphere. |
| Photophosphorylation | (Environmental Engineering) The synthesis of the energy storage compound adenosine triphosphate (ATP) from adenosine diphosphate (ADP) using solar energy. |