Metabolism
Metabolism is the sum of all of the chemical reactions that occur within a living cell. Metabolic studies began in the 1830s with the work of Justus von Liebig [German: 1802-1873], who believed that all physiology (life activity) could be explained in chemical and physical terms. Liebig developed a reliable technique to determine the proportions of elements in a compound, and used this technique to analyze hundreds of organic compounds.
Migration
Migration is the regular movement of animals from one place to another. It allows animals to avoid competition and take advantage of seasonal resources such as food and breeding sites.
People have been aware of migration since ancient times. For example, Aristotle noted that cranes, geese, and swans move to warmer places for the winter. But people often had odd explanations for the disappearance of certain animals at the end of a season. As late as the 1500s some naturalists believed that swallows hibernated underwater through the cold months. A 1703 essay hypothesized that migratory birds wintered on the Moon.
Lumbering
Lumbering is cutting down trees to provide wood for lumber (wood sawed into planks). Although tools called hand “axes” were made over a million years ago, they probably were weapons, not lumbing tools. Axes used for cutting wood first appeared in Europe at the end of the last ice age, almost 12,000 years ago. A thousand years later, as farming began, humans began to grind and polish stone axes, making stronger tools that can be sharpened. Beside axes, tools called adzes were made from ground stone. An adze has its sharp edge perpendicular to its handle and shapes wood into flat-sided beams can planks. Another tool, the saw, was made from flaked stone or chipped bone.
Motion
If you push something hard enough, it moves. Sometimes it keeps moving after you stop pushing. Drop it, and it moves without a push. Such experiences lead to our ideas about motion. Nevertheless, early scientists found motion hard to understand. Some early philosophers, such as Zeno [Greek: c. 490-c. 425 B.C.], argued that logically motion could not exist. Aristotle developed ideas about motion some 200 years after Zeno. He measured motion as speed (change of distance with time) and acceleration (change of speed). He correctly observed that objects accelerate-gain speed-as they fall, but he also made errors. For example, since he observed feathers falling more slowly than rocks, Aristotle concluded that falling heavy objects accelerate faster than light ones.
Nuclear Reactors
In 1938, Otto Hahn [German: 1879-1968] and Fritz Strassmann [German: 1902-1980] established that some large atomic nuclei can break apart, or undergo fission, releasing energy. Soon after, the U.S Government hired Enrico Fermi to develop a device to produce and control nuclear fission. Fermi succeeded on December 2, 1942. His “nuclear pile” –lumps of uranium and carbon interspersed with cadmium strips–was a step in producing materials for nuclear weapons, and it also released energy.
Earth’s Structure
People living around the Mediterranean Sea can observe volcanoes such as Vulcan, Stromboli, and Etna, which erupt almost continually. From experience with volcanoes, ancient people concluded that Earth’s interior contained fires, though there was no way to know whether Earth was solid rock or hollow. Read more