Thursday, March 13, 2008

Temperature

Temperature is a physical assets of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Specifically, temperature is a property of substance. Temperature is one of the major parameters of thermodynamics. On the microscopic scale, temperature is defined as the average energy of microscopic motions of a single atom in the system per degree of freedom. On the macroscopic scale, temperature is the exclusive physical property that determines the direction of heat flow between two objects placed in thermal contact. If no heat flow occurs, the two objects have the same temperature; otherwise heat flows from the hotter object to the colder object. These two basic principles are stated in the zeroth law and second law of thermodynamics, respectively. For a solid, these microscopic motions are principally the vibrations of its atoms about their sites in the firm. For an idyllic monatomic gas, the microscopic motions are the translational motions of the component gas particles

Temperature is measured with thermometers that may be calibrated to a range of temperature scales. In most of the world (except for the United States, Jamaica, and a few other countries), the degree Celsius scale is used for most warmth measuring purposes. The entire scientific world measures temperature using the Celsius scale and thermodynamic temperature using the kelvin scale, which is just the Celsius scale shifted downwards so that 0 K[1]= −273.15 °C, or absolute zero. Many engineering fields in the U.S., especially high-tech ones, also use the kelvin and degrees Celsius scales. However, the United States is the last major country in which the degree Fahrenheit temperature scale is used by most lay people, industry, popular meteorology, and government. Other engineering fields in the U.S. also rely upon the Rankine scale when working in thermodynamic-related disciplines such as incineration.

Monday, March 10, 2008

Amazon River

The Amazon hand basin, the largest drainage basin in the world, covers an area of some 6,915,000 square kilometres (2,670,000 sq mi), or some 40 percent of South America. It gathers its waters from 5 degrees north freedom to 20 degrees south freedom. Its most remote sources are found on the inter-Andean upland, just a short distance from the Pacific Ocean.

The area covered by the water of the River and its tributaries more than triples over the course of a year. In an average dry season 110,000 square kilometres (42,000 sq mi) of land are water-covered, while in the wet season the flooded area of the Amazon Basin rises to 350,000 square kilometres (135,000 sq mi). At its widest point the Amazon River can be 11 kilometres (7 mi) wide during the dry season, but during the rainy season when the Amazon floods the surrounding plains it can be up to 45 kilometres (28 mi) wide.

The quantity of fresh water released by the Amazon to the Atlantic Ocean is mammoth: up to 300,000 m³ per second in the showery season. The Amazon is liable for a fifth of the total volume of fresh water entering the oceans global. Offshore of the mouth of the Amazon, potable water can be drawn from the ocean while still out of sight of the coast, and the salinity of the ocean is notably lower a hundred miles out to sea.