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Showing posts with label law. Show all posts
Showing posts with label law. Show all posts

Monday, November 20, 2017

Newton's Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first.


Tuesday, May 17, 2016

Buys-Ballot Law

In the Northern Hemisphere, with the wind at your back, low pressure is to your left (and high pressure is to your right) because winds travel counterclockwise (cyclonic) around low pressure zones, again, in the Northern Hemisphere.

Wednesday, March 23, 2016

Wien's Displacement Law

Wien’s displacement law says that the wavelength of the maximum emitted radiation is inversely proportional to the absolute temperature (°K). In other words, hotter objects radiate more energy at shorter wavelengths than do cooler bodies at all wavelengths. This allows us to determine the temperature of other stars depending on its color. Something that glows blue hot is much warmer than one that glow red hot!






Stefan-Boltzmann Law

            Blackbodies are purely hypothetical bodies—they do not exist in nature—that emit the maximum possible radiation at every wavelength. The single factor that determines how much energy a blackbody radiates is its temperature. Although, the amount of radiation emitted by an object is not linearly proportional to its temperature which is where the Stefan-Boltzmann law comes into play. The blackbody version of the Stefan-Boltzmann law expresses that the intensity of energy radiated by a blackbody increases according to the fourth power of its absolute temperature.
I = σT4
where I denotes the intensity of radiation in watts per square meter, σ (Greek lowercase sigma) is the Stefan-Boltzmann constant (5.67 × 10−8 watts per square meter per K4), and T is the temperature of the body in kelvins.
            At any rate due to the fact that blackbodies do not exist in nature most liquids and solids can be treated as graybodies, meaning they emit some percent of the maximum amount of radiation possible at a given temperature. Which brings us to the graybody version of the Stefan-Boltzmann law that includes the emissivity factor, meaning that the electromagnetic energy emitted by any graybody will be some fraction of what would be emitted by a blackbody.
I = ƐσT4

That percent of energy radiated by a substance relative to that of a blackbody is considered emissivity (ε), ranging from just above zero to just below 100 percent. However, the atmosphere is an exception to this because emission depends on a number of factors (i.e. the amount of water vapor and other gases in the air). Still, we can say that the atmosphere is not a perfect emitter of radiation because it emits less radiation at any particular temperature than would a blackbody.





Laws of Thermodynamics


0th Law of Thermodynamics—if body A is in thermal equilibrium with body T, and so it body B, then A and B are in thermal equilibrium.

1st Law of Thermodynamics—a measure of heat transferred into a system will result in an increase in temperature and in the system’s ability to do work. In other words, energy is conserved property that is neither created nor destroyed but, may change form and travel from place to place. Or, in terms of an internal combustion engine in an automobile, the first law describes the underlying principle of what occurs in the cylinder.

Other forms of the First Law…




2nd Law of Thermodynamics—only in transferring heat from a warmer body to a cooler body can heat be converted into work, in a cyclical process. A cyclic process is a series of operations by which the state of the substance (working substance) changes but the substance is finally returned to its original state in all respects. In other words, heat is always transferred from regions of high temperature to regions of low temperature. Heat can be transferred by three processes…
1.    Conduction—the movement of heat through a substance without appreciable movement of the molecules.
2.    Convection—the transfer of heat by mixing of a fluid.
3.    Radiation—the transfer of energy by radiation that can occur through empty space.

Forms of the Second Law, considering the Carnot Cycle…

3rd Law of Thermodynamics—there is no finite series of steps that can get you to absolute zero. In other words, since absolute zero cannot be reached an engine cannot be perfectly efficient.


Conclusion—heat can be converted into work, in a cyclic process, but can only be perfectly efficient at absolute zero, which is unattainable. 

Tuesday, March 22, 2016

Ideal Gas Law / Equation of State

The ideal gas law combines Boyle’s law, Charles’ law and uses volume as the inverse of density. All gases are found to approximately follow this equation.


     Gases tend to expand when heated and become denser when cooled.
     Density increase + constant temperature = pressure increase

     Constant density + temperature increase = pressure increase