ScienceIQ.com

What Is Coral Bleaching?

Certain types of stressors, such as increased sea surface temperatures or toxic exposures to oil, can cause coral polyps to lose their pigmented zooxanthellae, or to 'bleach.' Bleaching occurs naturally and is caused by various environmental stresses, including increased or decreased light, reduced salinity, or in the case of mass bleaching, ...

Continue reading...

WhatIsCoralBleaching
Astronomy

GP-B: More Than Just a Pretty Face

Questions about the ways space, time, light and gravity relate to each other have been asked for eons. Theories have been offered, yet many puzzles remain to be solved. No spacecraft ever built has ... Continue reading

GPBMoreThanJustaPrettyFace
Medicine

Protozoa That Cause Disease

Diseases caused by protozoan parasites are among the leading causes of death and disease in tropical and subtropical regions of the world. Developing countries within these areas contain ... Continue reading

ProtozoaThatCauseDisease
Physics

Earth's Magnetism

Most ancient civilizations were aware of the magnetic phenomenon. Sailors in the late thirteenth century used magnetized needles floating in water as primitive compasses to find their way on the sea. ... Continue reading

EarthsMagnetism
Geology

Diamonds Improved by Irradiation?

Besides hardness and texture, probably the most fascinating aspect of gems is their color. There are so many different and wonderful clear and foggy gems with colors that span almost the complete ... Continue reading

IrradiationDiamond

Get the Point?

DiscusJavelinThe discus and javelin first appeared in ancient game competitions in 708 B.C. Javelin events included both target throwing and distance throwing using a sling. By 1780, the javelin was adopted as an event by the Scandinavians, and the current one-handed throwing style while running was adopted at this time. In 1953, a hollow javelin was developed in the United States by Franklin 'Bud' Held who also set a new world record. Since the javelin had a standard weight, the surface area was increased which augmented the javelin's flight capability and caused it to land horizontally. In 1966, the javelin was thrown over 100 meters (328 feet) by an athlete using a discus style turn before the throw. This throwing style was judged unsafe and thereafter banned by the International Amateur Athletic Federation (IAAF). The 100-meter mark was broken again in 1984. Subsequently, the IAAF adopted new rules to ensure shorter flight times and sport safety.

The modern javelin is designed with the center of pressure located behind the center of gravity. This generates a nose down pitching moment (the tendency to produce motion about a point or axis), which reduces the javelin's flight time. Although the center of pressure's location varies during the javelin's flight, it always remains behind the center of gravity. As a result, the nose of the javelin pitches down. This nose down orientation also guarantees that the javelin lands point first. A point first landing ensures a safer event. In addition, since the javelin can no longer slide across the ground, the distance can be measured with greater accuracy.

During flight, the javelin also spins about its longitudinal axis. At a rate as high as 25 revolutions per second, the spin stabilizes the javelin in flight. The javelin also experiences oscillation down its length during flight. Oscillation is detrimental to the flight and needs to be minimized by the thrower or by the materials used in the javelin. Modern javelins are made from steel, aluminum or aluminum alloy. Novice throwers use a less stiff javelin (which is more forgiving in training). As skill is developed, a stiffer javelin is used (straighter flight). The steel javelins are the stiffest and have less vibration than the aluminum models, while aluminum offers flexibility and may be easier to throw.