In the natural sciences an isolated system, as contrasted with a open system, is a physical system that does not interact with its surroundings. It obeys a number of conservation laws: its total energy and mass stay constant. They cannot enter or exit, but can only move around inside. An example is in the study of spacetime, where it is assumed that asymptotically flat spacetimes exist.
open system is one whose border is permeable to both energy and mass
Closed system: Can interchange energy and mechanical work with other outside systems but not matter.
Kepler's Laws of Planetary Motion are three mathematical laws that describe the motion of planets in the Solar System. German mathematician and astronomer Johannes Kepler (1571–1630) discovered them.
Kepler studied the observations of the legendarily precise Danish astronomer Tycho Brahe. Around 1605, Kepler found that Brahe's observations of the planets' positions followed three relatively simple mathematical laws.
Kepler's laws challenged Aristotelean and Ptolemaic astronomy and physics. His assertion that the Earth moved, his use of ellipses rather than epicycles, and his proof that the planets' speeds varied, changed astronomy and physics. Nevertheless, the physical explanation of the planets' behavior came almost a century later, when Isaac Newton was able to deduce Kepler's laws from Newton's own laws of motion and his law of universal gravitation, using classical Euclidean geometry. Other models of gravitation would give empirically false results.
Kepler's three laws are:
1. The orbit of every planet is an ellipse with the sun at one of the foci. An ellipse is characterized by its two focal points; see illustration. Thus, Kepler rejected the ancient Aristotelean, ptolemaic, and Copernican belief in circular motion.
2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit. This means that the planet travels faster while close to the sun and slows down when it is farther from the sun. With his law, Kepler rejected the Aristotelean astronomical theory that planets have uniform speed.
3. The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axes (the "half-length" of the ellipse) of their orbits. This means not only that larger orbits have longer periods, but also that the speed of a planet in a larger orbit is lower than in a smaller orbit.
GEOCENTRIC model of the universe is the theory that the Earth is at the center of the universe and the Sun and other objects go around it. Belief in this system was common in ancient Greece. It was embraced by both Aristotle and Ptolemy, and most Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circle the Earth. Similar ideas were held in ancient China.
Two common observations were believed to support the idea that the Earth is in the center of the Universe. The first is that the stars (including the Sun and planets) appear to revolve around the Earth each day, with the stars circling around the pole and those stars nearer the equator rising and setting each day and circling back to their rising point. The second is the common sense perception that the Earth is solid and stable; it is not moving but is at rest.
HELIOCENTRISM is the theory that the sun is at the center of the Solar System. The word came from the Greek (ήλιος Helios = sun and κέντρον kentron = center). Historically, heliocentrism is opposed to geocentrism and currently to modern geocentrism, which places the earth at the center. (The distinction between the Solar System and the Universe was not clear until modern times, but extremely important relative to the controversy over cosmology and religion.)
Although many early cosmologists such as Aristarchus speculated about the motion of the Earth around a stationary Sun, it was not until the 16th century that Copernicus presented a fully predictive mathematical model of a heliocentric system, which was later elaborated by Kepler and defended by Galileo, becoming the center of a major dispute.
rlp2008
