| Glossary | ||||||||||||||
| speed of light
— constant value of the speed that light (or electromagnetic radiation) travels in a vacuum. The speed of light has a value of c = 3.0×108 m/s. speed of sound — speed that a sound wave travels in a medium. The speed of sound is 343 m/s in air at 1 atmosphere and 21ºC. spontaneous emission — process by which an excited atom releases energy by producing a photon of light, causing an electron to transition from a higher to a lower energy state. spring — elastic device specifically designed to produce a controllable restoring force when it is deformed. spring constant — quantity representing the value of the restoring force exerted by a particular spring (or other elastic material) when it is stretched or compressed. Measured in units of force divided by length, or newtons per meter (N/m). standing wave — stationary wave pattern created by two identical waves traveling in opposite directions, such as on a vibrating string. state — particular configuration of all the elements in a system, usually in reference to a defined energy of the system. static electricity — buildup of electrical charge, either positive or negative, on the surface of an insulating material. static friction — friction force that occurs between two surfaces that are at rest with respect to each other. statistical mechanics — branch of physics that uses statistical analysis to relate the macroscopic properties of matter, such as temperature and pressure, to the microscopic behavior of collections of atoms or molecules. stimulated emission — process in which an atomic electron in an excited state interacting with an electromagnetic wave of a specific frequency drops to a lower energy level, thereby transferring its energy to the wave. streamline — imaginary line through a fluid tracing the path of motion followed by a particular element of mass within the fluid. | stress
— force per unit of cross-sectional area.
Stress has units of pressure, which are measured in pascals (Pa) or psi. strong nuclear force — strongest of the fundamental forces of nature and the force that is responsible for holding the protons and neutrons in an atom’s nucleus together. subtractive primary colors (CMYK) — three colors of pigments (cyan, magenta, and yellow) that absorb light and, when mixed in various proportions, can reflect any color. The “K” in CMYK refers to a black pigment used to create darker shades. superposition principle — when two or more waves overlap, the amplitude of the resulting wave is the sum of the amplitudes of the individual waves. supersonic — moving faster than the speed of sound, which is 343 m/s (767 mph) in air at standard temperature and pressure. surface area — number of square units that completely cover the exterior or exposed surface of an object. system — group of related and interacting objects and influences that we choose to investigate. A system can be open or closed. technology — designed world, including all inventions, devices, processes, and products developed by humans. Technology is the output of engineering. temperature — (1) measurement quantifying the degree of hot or cold of a substance; (2) average kinetic energy per molecule in a substance. Usually measured using either a relative scale (such as degrees Celsius or Fahrenheit) or an absolute scale (such as kelvins). tensile strength — stress value at which a solid material typically fails in tension. tension — force that pulls or stretches a material. Since tension is a force it has units of newtons (N). terminal velocity — speed at which air friction and weight become equal and downward acceleration ceases. Terminal velocity can also apply to motion through water or any other condition where friction increases with speed. | |||||||||||||
| ||||||||||||||
