ScienceIQ.com

What Are Stem Cells?

When an egg is fertilized by a sperm cell, it quickly becomes a single cell from which all cells of the body-to-be will be created. This 'mother of all cells' is what biologists call a totipotent stem cell, meaning that it has unlimited creative power. Within a few days, the totipotent stem cell begins a process of division into a hollow sphere (a ...

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StemCells
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
Biology

The Dogma of Life

Dogmas are authoritative tenets common in religion and philosophy. But in molecular biology? Molecular biology has a central dogma, proposed by Francis Crick in 1953, that says that genetic ... Continue reading

MolecularBiology
Engineering

A Quick Guide To Gliders

A glider is a special kind of aircraft that has no engine. Paper airplanes are the most obvious example, but gliders come in a wide range of sizes. Toy gliders, made of balsa wood or styrofoam, are an ... Continue reading

AQuickGuideToGliders
Engineering

Sundials, Ancient Clocks

The earliest and simplest form of sundial is the shadow stick. The time of day is judged by the length and position of the stick's shadow. Some nomadic peoples still use this method for timekeeping. ... Continue reading

SundialsAncientClocks

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.