Aerodynamics

Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with the difference being that gas dynamics applies to all gases. Understanding the motion of air (often called a flow field) around an object enables the calculation of forces and moments acting on the object. Typical properties calculated for a flow field include velocity,pressure, density and temperature as a function of position and time. By defining a control volume around the flow field, equations for the conservation of mass, momentum, and energy can be defined and used to solve for the properties. The use of aerodynamics through mathematicalanalysis, empirical approximations, wind tunnel experimentation, andcomputer simulations form the scientific basis for heavier-than-air flight.
Aerodynamic problems can be classified according to the flow environment.External aerodynamics is the study of flow around solid objects of various shapes. Evaluating the lift and drag on an airplane or the shock waves that form in front of the nose of a rocket are examples of external aerodynamics.Internal aerodynamics is the study of flow through passages in solid objects. For instance, internal aerodynamics encompasses the study of the airflow through a jet engine or through an air conditioning pipe.
Aerodynamic problems can also be classified according to whether the flow speed is below, near or above the speed of sound. A problem is called subsonic if all the speeds in the problem are less than the speed of sound, transonic if speeds both below and above the speed of sound are present (normally when the characteristic speed is approximately the speed of sound), supersonic when the characteristic flow speed is greater than the speed of sound, and hypersonic when the flow speed is much greater than the speed of sound. Aerodynamicists disagree over the precise definition of hypersonic flow; minimum Mach numbersfor hypersonic flow range from 3 to 12.
The influence of viscosity in the flow dictates a third classification. Some problems may encounter only very small viscous effects on the solution, in which case viscosity can be considered to be negligible. The approximations to these problems are called inviscid flows. Flows for which viscosity cannot be neglected are called viscous flows.

Final Fate.

The Death of a Star

In general, the larger a star, the shorter its life, although all but the most massive stars live for billions of years. When a star has fused all the hydrogen in its core, nuclear reactions cease. Deprived of the energy production needed to support it, the core begins to collapse into itself and becomes much hotter. Hydrogen is still available outside the core, so hydrogen fusion continues in a shell surrounding the core. The increasingly hot core also pushes the outer layers of the star outward, causing them to expand and cool, transforming the star into a red giant.

If the star is sufficiently massive, the collapsing core may become hot enough to support more exotic nuclear reactions that consume helium and produce a variety of heavier elements up to iron. However, such reactions offer only a temporary reprieve. Gradually, the star's internal nuclear fires become increasingly unstable - sometimes burning furiously, other times dying down. These variations cause the star to pulsate and throw off its outer layers, enshrouding itself in a cocoon of gas and dust. What happens next depends on the size of the core.

Average Stars Become White Dwarfs

For average stars like the Sun, the process of ejecting its outer layers continues until the stellar core is exposed. This dead, but still ferociously hot stellar cinder is called a a White Dwarf. White dwarfs, which are roughly the size of our Earth despite containing the mass of a star, once puzzled astronomers - why didn't they collapse further? What force supported the mass of the core? Quantum mechanics provided the explanation. Pressure from fast moving electrons keeps these stars from collapsing. The more massive the core, the denser the white dwarf that is formed. Thus, the smaller a white dwarf is in diameter, the larger it is in mass! These paradoxical stars are very common - our own Sun will be a white dwarf billions of years from now. White dwarfs are intrinsically very faint because they are so small and, lacking a source of energy production, they fade into oblivion as they gradually cool down.

This fate awaits only those stars with a mass up to about 1.4 times the mass of our Sun. Above that mass, electron pressure cannot support the core against further collapse. Such stars suffer a different fate as described below.

               

White Dwarfs May Become Novae

If a white dwarf forms in a binary or multiple star system, it may experience a more eventful demise as a nova. Nova is Latin for "new" - novae were once thought to be new stars. Today, we understand that they are in fact, very old stars - white dwarfs. If a white dwarf is close enough to a companion star, its gravity may drag matter - mostly hydrogen - from the outer layers of that star onto itself, building up its surface layer. When enough hydrogen has accumulated on the surface, a burst of nuclear fusion occurs, causing the white dwarf to brighten substantially and expel the remaining material. Within a few days, the glow subsides and the cycle starts again. Sometimes, particularly massive white dwarfs (those near the 1.4 solar mass limit mentioned above) may accrete so much mass in the manner that they collapse and explode completely, becoming what is known as a supernova.

               

Supernovae Leave Behind Neutron Stars or Black Holes

Main sequence stars over eight solar masses are destined to die in a titanic explosion called a supernova. A supernova is not merely a bigger nova. In a nova, only the star's surface explodes. In a supernova, the star's core collapses and then explodes. In massive stars, a complex series of nuclear reactions leads to the production of iron in the core. Having achieved iron, the star has wrung all the energy it can out of nuclear fusion - fusion reactions that form elements heavier than iron actually consume energy rather than produce it. The star no longer has any way to support its own mass, and the iron core collapses. In just a matter of seconds the core shrinks from roughly 5000 miles across to just a dozen, and the temperature spikes 100 billion degrees or more. The outer layers of the star initially begin to collapse along with the core, but rebound with the enormous release of energy and are thrown violently outward. Supernovae release an almost unimaginable amount of energy. For a period of days to weeks, a supernova may outshine an entire galaxy. Likewise, all the naturally occurring elements and a rich array of subatomic particles are produced in these explosions. On average, a supernova explosion occurs about once every hundred years in the typical galaxy. About 25 to 50 supernovae are discovered each year in other galaxies, but most are too far away to be seen without a telescope.

               

Neutron Stars

If the collapsing stellar core at the center of a supernova contains between about 1.4 and 3 solar masses, the collapse continues until electrons and protons combine to form neutrons, producing a neutron star. Neutron stars are incredibly dense - similar to the density of an atomic nucleus. Because it contains so much mass packed into such a small volume, the gravitation at the surface of a neutron star is immense. Like the White Dwarf stars above, if a neutron star forms in a multiple star system it can accrete gas by stripping it off any nearby companions. The Rossi X-Ray Timing Explorer has captured telltale X-Ray emissions of gas swirling just a few miles from the surface of a neutron star.

Neutron stars also have powerful magnetic fields which can accelerate atomic particles around its magnetic poles producing powerful beams of radiation. Those beams sweep around like massive searchlight beams as the star rotates. If such a beam is oriented so that it periodically points toward the Earth, we observe it as regular pulses of radiation that occur whenever the magnetic pole sweeps past the line of sight. In this case, the neutron star is known as a pulsar.

Black Holes

If the collapsed stellar core is larger than three solar masses, it collapses completely to form a black hole: an infinitely dense object whose gravity is so strong that nothing can escape its immediate proximity, not even light. Since photons are what our instruments are designed to see, black holes can only be detected indirectly. Indirect observations are possible because the gravitational field of a black hole is so powerful that any nearby material - often the outer layers of a companion star - is caught up and dragged in. As matter spirals into a black hole, it forms a disk that is heated to enormous temperatures, emitting copious quantities of X-rays and Gamma-rays that indicate the presence of the underlying hidden companion.

From the Remains, New Stars Arise

The dust and debris left behind by novae and supernovae eventually blend with the surrounding interstellar gas and dust, enriching it with the heavy elements and chemical compounds produced during stellar death. Eventually, those materials are recycled, providing the building blocks for a new generation of stars and accompanying planetary systems.

Black Holes.

According to the general theory of relativity, a black hole is a region of space from which nothing, including light, can escape. It is the result of the denting of spacetime caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black body in thermodynamics. Under the theory of quantum mechanics black holes possess a temperature and emit radiation through slow dissipation by anti-protons.

Despite its undetectable interior, a black hole can be observed through its interaction with matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space. Alternatively, when gas falls into a stellar black hole from a companion star or nebula, the gas spirals inward, heating to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and Earth-orbiting telescopes.

Astronomers have identified numerous stellar black hole candidates, and have also found evidence of supermassive black holes at the center of every galaxy. After observing the motion of nearby stars for 16 years, in 2008 astronomers found compelling evidence that a supermassive black hole of more than 4 million solar masses is located near the Sagittarius A region in the center of the Milky Way galaxy.

How Black Holes Form?

Most black holes are made when a giant star, called a supergiant, at least twenty times bigger than our own Sun dies, and leaves behind a mass that is at least one solar mass. Stars die when they run out of hydrogen or other nuclear fuel to burn and start to collapse.

A supergiant star's death is called a supernova. Stars are usually in equilibrium, which means they are making enough energy to push their mass outward against the force of gravity. When the star runs out of fuel to make energy, gravity takes over. Gravity pulls the center of the star inward very quickly (so quickly that it would have to be repeated several thousand times before it took up a single second), and it collapses into a little ball. The collapse is so fast and violent that it makes a shock wave, and that causes the rest of the star to explode outward. As the gravity pushes the star inward, the pressure in the center of star reaches to such an extreme level that it enables heavier molecules like iron and carbon to interact to release nuclear energy. The release of the energy from the star during a very short period of time (about one hour) is with such a high rate that it outshines an entire galaxy.

The ball in the center is so dense (a lot of mass in a small space, or volume), that if you could somehow scoop only one teaspoon of material and bring it to Earth, it would sink to the core of the planet. If the original star was large enough the densely packed ball is called a singularity, the core of a black hole, but if it was not it would become either a neutron star or a dwarf star.

Even without a supernova, a black hole will form any time there is a lot of matter in a small space, without enough energy to act against gravity and stop it from collapsing.

If supernovas are so bright, why do we not see them often? Actually, there are usually hundreds of years between naked-eye super nova sightings. It is because the period of being a super nova in a star life cycle is only a few hours out of the billions of years in a star's life span. The probability (chance) of looking at a star in sky and that being in super nova state is equal to the ratio of an hour over several billion years.

It is worth mentioning that all of the heavier materials like carbon, oxygen, all the metals, etc, that make the life on the earth possible and are ingredients of all living creatures, can only form in the extreme pressure at the center of a super nova. So we are all a remnant ash from one exploding star several billion years ago.

Black holes have also been found in the middle of every major galaxy in the universe. These are called supermassive black holes, and are the biggest black holes of all. They formed when the Universe was very young, and also helped to form all the galaxies.

Some black holes are also responsible for making things called quasars. A quasar occurs when a black hole consumes all the gas surrounding it. As the gas gets close to the black hole itself, it heats up from a process called friction, and glows so brightly that this light can be seen on the other side of the Universe. It is often brighter than the whole galaxy the quasar is in. When astronomers first found quasars, they thought they had found objects close to us. After using a measuring technique called red shift, they discovered these quasars were actually very far away in the universe.

The Big Big Bang.

The Big Bang is the name of a scientific theory that explains how the Universe started, and then made the groups of stars (called galaxies) we see today.

In the Big Bang theory, the universe begins as very hot, small and dense, with no stars, atoms, form, or structure (called a "singularity"). Then about 14 billion years ago. the space in the universe expanded very very quickly (like a big bang), and later atoms formed, and then the stars and their galaxies. The universe is still expanding today, and getting bigger, but colder.

As a whole, space is growing and the temperature is falling as time passes. Cosmology is the name given to how the universe began and how it has developed. Scientists that study cosmology agree the Big Bang theory matches what they have seen so far.

Fred Hoyle called the theory the "Big Bang" on his radio show. He did not believe the Big Bang was correct. Scientists who did not agree with him thought the name was funny and used it. Since then, Fred Hoyle's reasons for not liking the theory have been shown to be wrong.

Scientists base the Big Bang theory on many different observations. The most important is the redshift of very far away galaxies. Redshift is when the light from an object moving away from the earth looks like it has lost energy. Objects moving towards the earth look like their light has gained energy. This is because of the Doppler effect. The more redshift there is, the faster the object is moving away. By measuring the redshift we can work out how fast the object is moving. Since everything is moving away from everything else at a carefully measured rate, scientists calculate that everything was in the same place 13.7 billion years ago. Because most things become colder when they become bigger, the universe must have been very hot when it started.

Other observations that support the Big Bang theory are the amounts of chemical elements in the universe. Amounts of hydrogen, helium, and lithium seem to agree with the theory of the Big Bang. Scientists also have found "cosmic microwave background radiation". This radiation is radio waves that are everywhere in the universe. It is now very weak and cold, but a long time ago it was very strong and very hot.

The Big Bang might also have been the beginning of time. If the Big Bang was the beginning of time then there was no universe before the Big Bang. Other ideas that also have a Big Bang do not have a beginning of time at 13.7 billion years ago. Instead, these theories say that the beginning of the universe as we currently know it began at that time. Before then the universe may have been very different.

Mass–energy equivalence E=MC^2

In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept the total internal energy E of a body at rest is equal to the product of its rest mass m and a suitable conversion factor to transform from units of mass to units of energy. If the body is not stationary relative to the observer then account must be made for relativistic effects where m is given by the relativistic mass and E the relativistic energy of the body. Albert Einstein proposed mass–energy equivalence in 1905 in one of his Annus Mirabilis papers entitled "Does the inertia of a body depend upon its energy-content?" The equivalence is described by the famous equation:


where E is energy, m is mass, and c is the speed of light in a vacuum. The formula is dimensionally consistent and does not depend on any specific system of measurement units. For example, in many systems of natural units, the speed (scalar) of light is set equal to 1, and the formula becomes the identity E = mc²; hence the term "mass–energy equivalence".
The equation E = mc² indicates that energy always exhibits relativistic mass in whatever form the energy takes. Additionally, in systems which have no momentum (or are viewed in their center of momentum frame), then the equation E = mc² also continues to be correct. Mass–energy equivalence in either of these conditions means that mass conservation becomes a restatement, or requirement, of the law of energy conservation, which is the first law of thermodynamics. Mass–energy equivalence does not imply that mass may be "converted" to energy, and indeed implies the opposite. Modern theory holds that neither mass nor energy may be destroyed, but only moved from one location to another. Mass and energy are both conserved separately in special relativity, and neither may be created nor destroyed. In physics, mass must be differentiated from matter, a more poorly defined idea in the physical sciences. Matter, when seen as certain types of particles, canbe created and destroyed (as in particle annihilation or creation), but the precursors and products of such reactions retain both the original mass and energy, each of which remains unchanged (conserved) throughout the process. Letting the m in E = mc² stand for a quantity of "matter" (rather than mass) may lead to incorrect results, depending on which of several varying definitions of "matter" are chosen.
E = mc² has sometimes been used as an explanation for the origin of energy in nuclear processes, but mass–energy equivalence does not explain the origin of such energies. Instead, this relationship merely indicates that the large amounts of energy released in such reactions may exhibit enough mass that the mass-loss may be measured, when the released energy (and its mass) have been removed from the system.
Einstein was not the first to propose a mass–energy relationship (see the History section). However, Einstein was the first scientist to propose the E = mc² formula and the first to interpret mass–energy equivalence as a fundamental principle that follows from the relativistic symmetries of space and time.

Einstein's General Relativity

Einstein's general theory of relativity expanded on the special theory, explained gravity, and predicted phenomena such as black holes and the expanding universe.




















The Special and General Theories of Relativity
Einstein published his special theory in 1905 and his general theory in 1916. The special theory applies when no accelerations are involved and its effects become noticeable near the speed of light. The general theory applies when accelerations are involved and in the presence of strong gravitational fields. It explains gravity in terms of the curvature of four dimensional space-time.


Principle of Equivalence
General relativity is based on the principle of equivalence. The two statements of this principle are logically equivalent; either statement can be used to prove the other.


One statement relates to the concept of mass. Mass enters into Newton's second law, which states that the force needed to accelerate an object is proportional to its mass. This mass, the object's resistance to changing its velocity, is the inertial mass. Mass also enters into Newton's law of gravity. The gravitational force acting between two objects is proportional to their masses. This mass is the gravitational mass.


Is the inertial mass the same as the gravitational mass? Newton assumed that they were. Considering the question before concluding that they were, led Einstein to the general theory. The principle of equivalence states that the inertial mass equals the gravitational mass.


From this statement, it is possible to prove the other statement of this principle: Inertial forces are indistinguishable from gravitational forces. An inertial force is the apparent force felt when in an accelerating reference frame. When a car accelerates, the occupants feel pushed back into their seats. No real force is pushing them, but the car they are sitting in, their reference frame, is accelerating. So they feel an apparent inertial force pushing them back into their seats. The principle of equivalence states that it is not possible to distinguish between inertial forces and gravitational forces.


Light Affected by Gravity
Using the principle of equivalence, Einstein was able to show that light is affected by gravitational forces. To understand Einstein's reasoning, consider two enclosed rooms. One is at rest on the Earth's surface; the other is in space far from any gravitational forces but accelerating at exactly the same rate objects fall near Earth's surface. On Earth, the Earth's gravity causes objects to fall and have weight. In the accelerating room, objects will also fall and apparently have weight because the room is accelerating. It is an accelerating reference frame, so objects in the room experience an inertial force. From the principle of equivalence, it is impossible to distinguish between the gravitational force acting on objects in the room on Earth and the inertial force acting on objects in the accelerating room in space.


Consider a light beam shining across the accelerating room. Because the room is accelerating the light beam will strike the opposite wall slightly lower than its starting level. Inertial forces acts on the light beam. Because they are not distinguishable from gravitational forces the light beam should experience exactly the same effect in the room near Earth's surface. A gravitational force affects a light beam just as an inertial force does.


Geometric Nature of Gravity
Light has no mass, so Newtonian gravity predicts light is not affected by gravity. However Einstein concluded that light is affected by gravity and derived a new theory of gravity.


Einstein visualized gravity as a manifestation of the curvature of space-time - the three space dimensions and a fourth time dimension. Most of us cannot visualize a curvature of four dimensional space-time, so visualize a curved two dimensional rubber sheet. Placing a mass on the rubber sheet curves it downward like space-time curves in the presence of a mass. On such a rubber sheet a small mass can circle around the curvature produced by a large mass, just as planets orbit the Sun. Or a mass can roll straight downward just as an object falls to the Earth.


Einstein explained gravity as a result of the curvature of space-time near the presence of a mass. The differences between general relativity and Newton's law of gravity only become noticeable when the gravitational force is very strong.


Einstein's general theory of relativity is one of the crowning intellectual achievements of the 20th century and led to such predictions as black holes, gravitational lenses, and the expanding universe. So far it has passed every experimental test with flying colors.

The Philosophy of Science.

"Science is simply common sense at its best"

Thomas Huxley~

Science has many definitions but is often perceived as the human effort to understand the history of the natural world and how the natural world works. Science is broken down into two key components being the study of natural science and the philosophy of science. Natural science is distinctly known as biology, chemistry, physics and the study of the earth. The philosophy of science is concerned with the assumptions, foundations, and implications of science. 

Everyone at one point or another studies science. Whether it is in public school, university or everyday life. The problem is humanity only gives recognition to a certain amount of individuals who have either made a profession by teaching science, or are famous philosophers. It is impossible to pin point one group of citizens or an individual because numerous people study science. 

Even though science has a long history in ancient Egypt and Mesopotamia, it is unquestionable that modern science emerged in Western Europe. (American scholar| January 1st, 1977, Grant Edward) The reason for this momentous conclusion is Western Europe had a tremendous knowledge of science that separated Western culture from other contemporary societies. Even though humanity has apparent evidence that the establishment of science began in Western Europe philosophers believe science began when mankind wondered how/why anything is the way it is. 

Science is one of the most influential tools know to society. Science is vital and crucial to civilization because it allows humanity to solve unknown questions with solid facts. Science provides humans skills to analyze and think logically. Everything humans do has a connection to science, whether it be driving your car or typing on a computer. Basically without science the human race would die.