Sunday, October 28, 2007

Bullet

A bullet is a solid projectile propelled by a firearm or air gun and is normally made from metal (usually lead). A bullet (in contrast to a shell) does not contain explosives, and damages the intended target solely by imparting kinetic energy upon impact. Modern bullets for firearms are usually part of a cartridge, also known as a round. In contrast, bullets for air guns are not part of a cartridge. The word "bullet" is sometimes used to refer to the combination of bullet, case, gunpowder and primer more properly known as a cartridge or round.[1]; the Oxford English Dictionary definition of a bullet is "a projectile of lead ... for firing from a rifle, revolver etc."

Tuesday, October 16, 2007

The facts about Mercury

Mercury is the nearby planet to the Sun and the eighth biggest. Mercury is somewhat smaller in diameter than the moons Ganymede and Titan but more than twice as enormous.

Mercury's orbit is extremely eccentric; at perihelion it is just 46 million km from the Sun but at aphelion it is 70 million. The position of the perihelion processes about the Sun at a very slow rate. 19th century astronomers made extremely careful observations of Mercury's orbital parameters but could not sufficiently explain those using Newtonian mechanics. The tiny differences between the observed and predicted values were a slight but nagging problem for many decades. It was thought that one more planet (sometimes called Vulcan) slightly nearer to the Sun than Mercury might account for the discrepancy. But in spite of much effort, no such planet was found. The real reply turned out to be much more dramatic: Einstein's General Theory of Relativity! Its right prediction of the motions of Mercury was a main factor in the early acceptance of the theory.

Mercury is greatly denser than the Moon. Mercury is the second densest most important body in the solar system, after Earth. Actually Earth's density is due in part to gravitational density; if not for this, Mercury would be denser than Earth. This signifies that Mercury's dense iron core is comparatively larger than Earth, probably comprises the greater part of the planet. Mercury therefore has only a comparatively thin silicate mantle and crust.

Mercury's inner is dominated by a big iron core whose radius. The silicate outer shell (analogous to Earth's mantle and crust) is just thick. At least some of the core is perhaps molten. Mercury truly has an extremely thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly flee into space. Thus on the contrary, to the Earth and Venus whose atmospheres are stable, Mercury's atmosphere is always being replenished.

Monday, October 08, 2007

Traffic Claming

Traffic calming is a set of strategies used by urban planners and traffic engineers which aims to slow down traffic and get better safety for pedestrians and bicyclists, although some of these features can also be hazardous to cyclists. It is now comparatively common in Europe, especially Northern Europe; less so in North America.Traffic calming has conventionally been justified on the grounds of pedestrian safety and reduction of noise and local air pollution which are side effects of the traffic. However, it has become more and more apparent that streets have many social and recreational functions which are severely impaired by fast car traffic. For much of the twentieth century, streets were designed by engineers who were charged only with ensuring traffic flow and not with development other functions of streets. The rationale for traffic reassuring is now broadening to include designing for these functions.