An extremely important concept in the development of mechanics is that of momentum. The momentum of a body is defined as the product of its mass by its velocity. We shall use the symbol p to denote the momentum of a body. The momentum of a body is a vector quantity, for it is the product of mass, a scalar, by velocity, a vector. While momentum and kinetic energy are compounded of the same two ingredients, mass and velocity, they are quite different concepts, and one aspect of their difference may be seen in the fact that momentum is a vector while energy is a scalar quantity

Katz, Robert

Semat, Henry

English

DigitalCommons@University of Nebraska

\u3ci\u3ePhysics\u3c/i\u3e, Chapter 10: Momentum and Impulse

In the passage of a beam of light through a medium, some of the radiant energy is absorbed and is transformed into internal energy, while some of it is scattered in all directions. The oscillating electric field associated with the light wave sets some of the electrons of the medium into oscillation, thus giving up some of its energy, and these oscillating electrons subsequently reradiate energy as scattered electromagnetic radiation. Scattering therefore takes place only in the presence of matter. The color of the sky is due to the small amount of scattering of sunlight by the molecules of the air. At high altitudes the number of scattering particles diminishes, and the sky is darker. In the stratosphere the sky appears almost black. The molecules of the air are more effective in scattering short wavelengths, so that the scattered light appears blue. Since the shorter wavelengths are scattered from the direct beam, the beam appears redder as it passes through larger thicknesses of air. It is for this reason that the setting sun looks redder than the noonday sun. The scattering of light by the air is responsible for twilight. In microwave communications the distance between transmitting and receiving antennae is limited by the curvature of the earth, because of the straight-line propagation of electromagnetic waves. By transmitting a stronger initial signal and detecting the scattered microwaves, it has been possible to reduce the number of transmitting and receiving stations in the microwave communications network by increasing the distance between relay stations beyond the line of sight

\u3ci\u3ePhysics\u3c/i\u3e, Chapter 37: Reflection and Refraction

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Temperature is one of the fundamental concepts of physics. We are all able to recognize that some bodies are hotter than others, but our temperature sense is qualitative rather than quantitative and is capable of only a limited range. The sense of touch can frequently be used to distinguish between hotter and colder objects, provided that these lie in a temperature range consistent with the stability of human tissue. Even within this range the sense of touch is often unreliable as a measure of temperature.  The metal bracket holding a wooden rail may feel much colder to the touch than the railing itself, even though both are at the same temperature. It is a matter of common observation that some of the physical properties of many substances are altered when the temperature is changed. The volume or the pressure of a gas increases when the temperature is raised. The length of a copper rod changes with changing temperature. Some of the electric and magnetic properties of substances vary with changes in temperature. The changes that take place in these physical properties can be used to measure the changes in temperature which produced them

\u3ci\u3ePhysics\u3c/i\u3e, Chapter 14: Temperature

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1145&amp;context=physicskatz

\u3ci\u3ePhysics\u3c/i\u3e, Chapter 10: Momentum and Impulse

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DigitalCommons@University of Nebraska

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UNL | Libraries

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