SORASORACLASSES: IV Sez. A-B

TEACHERS: ANNARITA SBARDELLA

EMILIANA MANCINIVINCENZO RECCHIA

Power Point Presentation realized by: Lorenzo Corsetti (Class VA)Cristiano Diamanti (Class VA) Francesco D’Orazio (Class VA)

LICEO SCIENTIFICO STATALE "LEONARDO DA VINCI" SORA – ITALYCOMENIUS 1.3

“ENCOHAN - ENERGY IN THE CONSUMERS’ HANDS”2005 - 2008

TEACHERS:ANNARITA SBARDELLAEMILIANA MANCINIVINCENZO RECCHIA

CLASSES: IV Sez. A-B

LICEO SCIENTIFICO STATALE "LEONARDO DA VINCI" SORA – ITALYCOMENIUS 1.3

“ENCOHAN - ENERGY IN THE CONSUMERS’ HANDS “2005 - 2008

“ENCOHAN” PROJECT MEETING IN HUNGHERY: (6th November / 11th November 2006)

Teachers: Emiliana Mancini Vincenzo Recchia

“ENCOHAN” PROJECT MEETING IN POLAND:

(25th March / 1st April 2007) Teachers: Annarita Sbardella (Coordinator)

Vincenzo Recchia

Students: Francesca Fornari (Class IVA) Martina Liburdi (Class IVA) Luca Lombardi (Class IVA) Luigi Recchia (Class IVA) Chiara Iafrate (Class IVB) Alessia Pantano (Class IVB) Ilaria Urbani (Class IVB)

Silvia Venditti (Class IVB)

DRINKING BIRD

Drinking birds are thermodinamically powered toy heat engines that mimick the motions of a bird drinking from a fountain or other water source. They are also known as happy, dippy, dipping, tippy, tipping, sippy, sipping, dip-dip or dunking birds.Construction and materials:A drinking bird consists of two glass bulbs, joined by a tube (the bird's neck). The tube extends nearly all the way into the bottom bulb but does not extend into the top. The space inside is typically filled with coloured dichloromethane(also known as methylene chloride).Air is removed from the apparatus, so the space inside the body is filled by dichloromethane vapour. The upper bulb has a "beak" attached, which along with the head, is covered in a felt like material. The bird is typically decorated with paper eyes, a blue top hat (plastic) and a single green tail feather. The whole setup is pivoted on a variable point on the neck.The drinking bird illustrates the conversion of thermal energy into mechanical energy. The head of the bird is coated with a fuzzy material, and is initially soaked in water so that it will begin to cool by evaporation.

Drinking birds are thermodinamically powered toy heat engines that mimick the motions of a bird drinking from a fountain or other water source. They are also known as happy, dippy, dipping, tippy, tipping, sippy, sipping, dip-dip or dunking birds.Construction and materials:A drinking bird consists of two glass bulbs, joined by a tube (the bird's neck). The tube extends nearly all the way into the bottom bulb but does not extend into the top. The space inside is typically filled with coloured dichloromethane(also known as methylene chloride).Air is removed from the apparatus, so the space inside the body is filled by dichloromethane vapour. The upper bulb has a "beak" attached, which along with the head, is covered in a felt like material. The bird is typically decorated with paper eyes, a blue top hat (plastic) and a single green tail feather. The whole setup is pivoted on a variable point on the neck.The drinking bird illustrates the conversion of thermal energy into mechanical energy. The head of the bird is coated with a fuzzy material, and is initially soaked in water so that it will begin to cool by evaporation.

This provides the temperature difference from head to tail necessary to run the heat engine. As the head cools, the colored fluid is observed to rise up from the bottom of the bird through the neck, gradually shifting the center of gravity of the bird toward its head. The bird bends at the hips and dips its bill into a glass of water (thus keeping the head wet and cooler than the tail). As the fluid continues to rise into the head, the fluid level in the bottom of the bird eventually drops below the end of the connecting tube. This allows vapor to be pulled up through the neck to equilibrate the pressure. The fluid runs back down into the bottom of the bird, the bird stands up again, and the cycle repeats indefinitely.

The drinking bird is basically a heat engine that exploits a temperature differential to convert heat energy to kinetic energy and perform mechanical work. Like all heat engines, the drinking bird works through a thermodynamic cycle. The initial state of the system is a bird with a wet head oriented vertically with an initial oscillation on its pivot.

DRINKING BIRD

DRINKING BIRD

The cycle operates as follows:• The water evaporates from the head.• Evaporation lowers the temperature of the glass head. • The temperature drop causes some of the dichloromethane

vapor in the head to condense.• The lower temperature and condensation together cause the

pressure to drop in the head (ideal gas law). • The pressure differential between the head and base causes

the liquid to be pushed up from the base. • As liquid flows into the head, the bird becomes top heavy and

tips over during its oscillations. • When the bird tips over, the bottom end of the neck tube

rises above the surface of the liquid. • A bubble of vapor rises up the tube through this gap,

displacing liquid as it goes • Liquid flows back to the bottom bulb, and vapor pressure

equalizes between the top and bottom bulbs • The weight of the liquid in the bottom bulb restores the bird

to its vertical position.

If a glass of water is placed so that the beak dips into it on its descent, the bird will continue to absorb water and the cycle will continue as long as there is enough water in the glass to keep the head wet. However, the bird will continue to dip even without a source of water, as long as the head is wet, or as long as a temperature differential is maintained between the head and body. This differential can be generated without evaporative cooling in the head -- for instance, a heat source directed at the bottom bulb will create a pressure differential between top and bottom that will drive the engine. The ultimate source of energy is heat in the surrounding environment -- the toy is not a perpetual motion machine.

DRINKING BIRD

1) Heat engineA heat engine is a physical or theoretical device that converts thermal energy to mechanical output. The mechanical output is called work, and the thermal energy input is called heat. Heat engines typically run on a specific thermodynamic cycle. Heat engines are often named after the thermodynamic cycle they are modeled by. They often pick up alternate names, such as gasoline/petrol, turbine, or steam engines. Heat engines can generate heat inside the engine itself or it can absorb heat from an external source. Heat engines can be open to the atmospheric air or sealed and closed off to the outside (Open or closed cycle).In engineering and thermodynamics, a heat engine performs the conversion of heat energy to mechanical work by exploiting the temperature gradient between a hot "source" and a cold "sink". Heat is transferred from the source, through the "working body" of the engine, to the sink, and in this process some of the heat is converted into work by exploiting the properties of a working substance (usually a gas or liquid).

THE PHISICS AROUND :

THE PHISICS AROUND :

Figure 1: Heat engine diagramHeat engines are often confused with the cycles they attempt to mimic. Typically when describing the physical device the term 'engine' is used. When describing the model the term 'cycle' is used.In thermodinamics, heat engines are often modeled using a standard engineering model such as the Otto cycle (4-stroke/2-stroke). Actual data from an operating engine, one is called a indicator diagram, is used to refine the model. All modern implementations of heat engines do not exactly match the thermodynamic cycle they are modeled by. One could say that the thermodynamic cycle is an ideal case of the mechanical engine. One could equally say that the model doesn't quite perfectly match the mechanical engine. However, much benefit is gained from the simplified models, and ideal cases they may represent.

THE PHISICS AROUND :

In general terms, the larger the difference in temperature between the hot source and the cold sink, the larger is the potential thermal efficiency of the cycle. On Earth, the cold side of any heat engine is limited to close to the ambient temperature of the environment, or not much lower than 300 kelvins, so most efforts to improve the thermodynamic efficiencies of various heat engines focus on increasing the temperature of the source, within material limits.

The efficiency of various heat engines proposed or used today ranges from 3 percent (97 percent waste heat) for the OTEC ocean power proposal through 25 percent for most automotive engines, to 35 percent for a supercritical coal plant, to about 60 percent for a steam-cooled combined cycle gas turbine. All of these processes gain their efficiency (or lack thereof) due to the temperature drop across them.

OTEC uses the temperature difference of ocean water on the surface and ocean water from the depths, a small difference of perhaps 25 degrees Celsius, and so the efficiency must be low. The combined cycle gas turbines use natural-gas fired burners to heat air to near 1530 degrees Celsius, a difference of a large 1500 degrees Celsius, and so the efficiency can be large when the steam-cooling cycle is added in:

THE PHISICS AROUND :

Thermodynamic cycles:

Atkinson cycleBrayton/Joule cycleCarnot cycle Combined cycle Crower cycle Diesel cycle Ericsson cycle Hirn cycle Kalina cycle Lenoir cycle Linde-Hampson cycle Miller cycle Mixed/Dual Cycle Otto cycle Rankine cycle Scuderi cycle

Figure 1: Heat engine diagram

Examples of everyday heat engines include: the steam engine, the diesel engine, and the gasoline (petrol) enginein an automobile. A common toy that is also a heat engine is a drinking bird. All of these familiar heat engines are powered by the expansion of heated gases. The general surroundings are the heat sink, providing relatively cool gases which, when heated, expand rapidly to drive the mechanical motion of the engine.It is important to note that although some cycles have a typical combustion location (internal external), they often can be implemented as the other combustion cycle. For example, John Ericsson developed an external heated engine running on a cycle very much like the earlier Diesel cycle. In addition, the externally heated engines can often be implemented in open or closed cycles.What this boils down to is there are thermodynamic cycles and a large number of ways of implementing them with mechanical devices called engines.

THE PHISICS AROUND

2) Evaporation and condensation EVAPORATION:

Water condenses into visible droplets after evaporating from a cup of hot tea

Evaporation is the process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state (the equivalent process in solids is known as sublimation). It is the opposite process of condensation. Evaporation is exclusively a surface phenomena and should not be confused with boiling. Most notably, for a liquid to boil, its vapor pressure must equal the ambient pressure, whereas for evaporation to occur, this is not the case.The vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor are in dynamic equilibrium.

THE PHISICS AROUND

In chemistry and physics, vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. All solids and liquids have a tendency to evaporate to a gaseous form, and all gases have a tendency to condense back. At any given temperature, for a particular substance, there is a partial pressure at which the gas of that substance is in dynamic equilibrium with its liquid or solid forms. This is the vapor pressure of that substance at that temperature. In meteorology, the term vapor pressure is used to mean the partial pressure of water vapor in the atmosphere, even if it is not equilibrium, and the equilibrium vapor pressure is specified as such. Meteorologists also use the term saturation vapor pressure to refer to the equilibrium vapor pressure of water or brine above a flat surface, to distinguish it from equilibrium vapor pressure which takes into account the shape and size of water droplets and particulates in the atmosphere.

THE PHISICS AROUND

Vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of molecules and atoms to escape from a liquid or a solid. A substance with a high vapor pressure at normal temperatures is often referred to as volatile. The higher the vapor pressure of a material at a given temperature, the lower the boiling point.The vapor pressure of any substance increases non-linearly with temperature according to the Clausius-Clapeyron relation. The boiling point of a liquid is the temperature where the vapor pressure equals the ambient atmospheric pressure. At the boiling temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form bubbles inside the bulk of the substance. Evaporation is a critical component of the water cycle, which is responsible for clouds and rain. Solar energy drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration.

THE PHISICS AROUND

CONDENSATION:

Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. Condensation commonly occurs when a vapor is cooled to a liquid, but can also occur if a vapor is compressed (i.e., pressure on it increased) into a liquid, or undergoes a combination of cooling and compression. Liquid which has been condensed from a vapor is called condensate. A device or unit used to condense vapors into liquid is called a condenser. Condensers are typically coolers or heat exchangers which are used for various purposes, have various designs, and come in many sizes ranging from rather small (hand-held) to very large.Condensation of vapor of liquid is the opposite of evaporation or boiling and is an exothermic process, meaning it releases heat. The water seen on the outside of a cold glass on a hot day is condensation.

THE PHISICS AROUND

THE PHISICS AROUND

CONDENSATION OF WATER IN NATURE:

Dew on a spider web

Water vapor from air which naturally condenses on cold surfaces into liquid water is called dew. Water vapor will only condense onto another surface when that surface is cooler than the temperature of the water vapor, or when the water vapor equilibrium in air, i. e. saturation humidity, has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface.

The water molecule brings a parcel of heat with it. In turn, the temperature of the atmosphere drops very slightly. In the atmosphere, condensation of water vapour is what produces clouds. The dew point of an air parcel is the temperature to which it must cool before condensation in the air begins to form.Also, a net condensation of water vapor occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. Deposition is a type of condensation. Frost and snow are examples of deposition (or sublimation). Deposition is the direct formation of ice from water vapor.

THE PHISICS AROUND

Condensation on a cold bottle of water

APPLICATIONS OF CONDENSATION:Because condensation is a naturally occurring phenomenon, it can often be used to generate water in large quantities for human use. In fact, there are many structures that are made solely for the purpose of collecting water from condensation, such as fog fences, air wells and dew ponds. Such systems can often be used to retain soil moisture in areas where active desertification is occurring. In fact, certain organizations use education about water condensers in efforts to effectively aid such areas.

THE PHISICS AROUND

CONDENSATION IN BUILDINGS:Condensation is the most common form of dampness encountered in buildings. In buildings the internal air can have a high level of relative humidity due to the activity of the occupants (e.g. cooking, drying clothes, breathing etc...). When this air comes into contact with cold surfaces such as windows and cold walls it can condense, causing dampness.

3) Ideal gas law

THE PHISICS AROUND

The ideal gas law is the equation of state of a hypothetical ideal gas, first stated by Benoît Paul Émile Clapeyron in 1834.The state of an amount of gas is determined by its pressure, volume, and temperature according to the equation:

where:

is the pressure [PAL]

is the volume [m ]3

is the amount of substance of gas [mol],

is the gas constant 8.3143 m3·Pa·K-1·mol-1, and

is the temperature in kelvins [K].

The ideal gas constant (R) is dependent on what units are used in the formula. The value given above, 8.314472, is for the SI units of pascal-cubic meters per mole-kelvin. Another value for R is 0.082057 L atm mol-1 K-1)The ideal gas law is the most accurate for monatomic gases and is favored at high temperatures and low pressures. It does not factor in the size of each gas molecule or the effects of intermolecular attraction. The more accurate Van der Waals equation takes these into consideration.

THE PHISICS AROUND

Alternate formsConsidering that the number of moles (n) could also be given in mass, sometimes you may wish to use an alternate form of the ideal gas law. This is particularly useful when asked for the ideal gas law approximation of a known gas. Consider that the number of moles (n) is equal to the mass (m) divided by the molar mass (M), such that:

Then, replacing n gives: in statistical mechanics, and is often derived from first principles:

THE PHISICS AROUND

Here, kb is Boltzmann's constant, and N is the actual number of molecules, in contrast to the other formulation, which uses n, the number of moles. This relation implies that Nkb = nR, and the consistency of this result with experiment is a good check on the principles of statistical mechanics.

From here we can notice that for an average particle mass of μ times the atomic mass of Hydrogen,

THE PHISICS AROUND

and since ρ = m / V, we find that the ideal gas law can be re-written as:

PROOF:EmpiricalThe ideal gas law can be proved using Royle,Charles and Gay-Lussac laws.

Consider an amount of gas. Let its initial state be defined as:volume = v0 pressure = p0 temperature = t0

If this gas now undergoes an isobaric process, its state will change:

volume:

pressure

temperature

THE PHISICS AROUND

THE PHISICS AROUND

If it then undergoes an isothermal process:

Where:

p = final pressure v = final volume T = final temperature (= t')

So:

Where:

THE PHISICS AROUND

termed R, is the universal gas constant

Using this notation we get:

And multiplying both sides of the equation by n (numbers of moles):

Using the symbol V as a shorthand for nv (volume of n moles) we get:

TheoreticalThe ideal gas law can also be derived from first principles using the kinetic theory of gases, in which several simplifying assumptions are made, chief amongst which is that the molecules, or atoms, of the gas are point masses, possessing mass but no significant volume.

THE PHISICS AROUND

LEVITRON

The LEVITRON is formed by a top that hangs above a base while is spinning. The 'antigravity' force that repels the top from the base is magnetism. Both the top and the heavy slab inside the base box are magnetized, but oppositely. Think of the base magnet with its north pole pointing up, and the top as a magnet with its north pole pointing down. The principle is that two similar poles (e.g., two norths) repel and that two opposite poles attract, with forces that are stronger when the poles are closer. There are four magnetic forces on the top: on its north pole, repulsion from the base's north and attraction from the base's south, and on its south pole, attraction from the base's north and repulsion from the base's south. Because of the way the forces depend on distance, the north-north repulsion dominates, and the top is magnetically repelled. It hangs where this upward repulsion balances the downward force of gravity, that is, at the point of equilibrium where the total force is zero. 

As well as providing a force on the top as a whole, the magnetic field of the base gives a torque tending to turn its axis of spin. If the top were not spinning, this magnetic torque would turn it over. Then its south pole would point down and the force from the base would be attractive - that is, in the same direction as gravity - and the top would fall. When the top is spinning, the torque acts gyroscopically and the axis does not overturn but rotates about the (nearly vertical) direction of the magnetic field. This rotation is called precession. With the LEVITRON, the axis is nearly vertical and the precession is visible as a shivering that gets more pronounces as the top slows down. For the top it remain suspended, equilibrium alone is not enough. The equilibrium must also be stable , so that a slight horizontal or vertical displacement produces a force pushing the top back toward the equilibrium point.

LEVITRON

For the LEVITRON, stability is difficult to achieve. It depends on the fact that as the top moves sideways, away from the axis of the base magnet, the magnetic field of the base, about which the top's axis precessed, deviates slightly from the vertical. If the top precessed about the exact vertical, the physics of magnetic fields would make the equilibrium unstable. Because the field is so close to vertical, the equilibrium is stable only in a small range of heights - between about 1.25 inches and 1.75 inches above the center of the base. (between 2.5 and 3.0 inches for Fascinations' new Super LEVITRON). The Earnshaw theorem is not violated by the behavior of the LEVITRON. That theorem states that no static arrangements of magnetic (or electric) charges can be stable, alone or under gravity. It does not apply to the LEVITRON because the magnet (in the top ) is spinning and so responds dynamically to the field from the base.

LEVITRON

The weight of the top and the strength of magnetization of the base and the top determine the equilibrium height where magnetism balances gravity. This height must lie in the stable range. Slight changes of temperature alter the magnetization of the base and the top. (as the temperature increases, the directions of the atomic magnets randomize and the field weakens). Unless the weight is adjusted to compensate, the equilibrium will move outside the stable range and the top will fall. Because the stable range is so small, this adjustment is delicate - the lightest washer is only about 0.3% of the weight of the top.The top spins stable in the range from about 20 to 35 revolutions per second (rps). It is completely unstable above 35-40 rps and below 18 rps. After the top is spun and levitated, it slows down because of air resistance. After a few minutes it reaches the lower stability limit (18 rps) and falls.

LEVITRON

The spin lifetime of the LEVITRON can be extended by placing it in a vacuum. In a few vacuum experiments that have been done the top fell after about 30 minutes. Why it does so is not clear; perhaps the temperature changes, pushing the equilibrium out of the stable range; perhaps there is some tiny residual long-term instability because the top is not spinning fast enough; or perhaps vibrations of the vacuum equipment jog the field and gradually drive the precession axis away from the field direction. Levitation can be greatly prolonged by blowing air against an appropriately serrated air collar placed around the top's periphery so as to maintain the spin frequency in the stable range.

LEVITRON

Recently a LEVITRON top was kept rotating for several days in this way. But the most successful means to prolong the top's levitation is with Fascinations' new PERPETUATOR, an electro-magnetic pulsed device which can keep the top levitating for many days or even weeks. In recent decades, microscopic particles have been studied by trapping them with magnetic and/or electric fields. There are several sorts of traps. For example, neutrons can be held in a magnetic field generated by a system of coils. Neutrons are spinning magnetic particles, so the analogy of such a neutron trap with the LEVITRON is close.

LEVITRON

THE PHISICS AROUND

1) Magnetism:

Speaking well about Homer is not a thing you have mastered, it's a divine power that moves you, as a "Magnetic" stone moves iron rings. (That's what Euripides called it; most people call it "Heraclian".) This stone not only pulls those rings, if they are iron, it also puts power in the rings, so they in turn can do just what the stone does - pull other rings - so that there is sometimes a very long chain of iron pieces, hanging from one another. And the power in all of them depends on this stone. - Socrates in Plato's "Ion" c. 380 BC

Magnetism has been known since ancient times. The magnetic property of lodestone (Fe3O4) was mentioned by the Greek philosopher Thales (c. 500 BC), and the Greeks called this mineral "Magnetic", after the province of Magnesia in Thessaly where it was commonly found. It was also found in the nearby province of Heraclia, which is presumably why Socrates says that most people called the stone "Heraclian". Apparently we have the great dramatist Euripides to thank for not having to pronounce the electro-heraclian field. About 1000 AD the Chinese began to use lodestone as a compass for finding directions on land, and soon afterwards Muslim sailors were using compasses to navigate at sea. Europeans began using magnetic compasses for navigation around 1200 AD, probably bringing the idea back from the Crusades.

THE PHISICS AROUND

THE PHISICS AROUND

The first scientific study of magnets was apparently by the English physician William Gilbert in 1600, who is credited with "discovering" that the Earth itself is a magnet. After Gilbert, the subject languished for almost 200 years, as the attention of most scientists turned to gravitation and working out the consequences of Newton's great synthesis of dynamics and astronomy. Not until 1785 was the subject taken up again, first by the Frenchman Charles Coulomb, then by Poisson, Oersted, Ampere, Henry, Faraday, Weber, and Gauss, culminating in Maxwell's classical synthesis of electromagnetic theory in 1875. However, despite the great achievements of these scientists, no satisfactory understanding of the various kinds of magnetic behavior exhibited by different materials was achieved. Only with the advent of quantum mechanics in the 1920's did it become possible to give a coherent account of the main magnetic properties of materials. It's a surprisingly complex subject, but we can give a broad outline of the modern explanations of magnetic phenomena.

The three main types of magnetic behavior exhibited by material substances are called diamagnetism, paramagnetism, and ferromagnetism. The first two can be explained in terms of the magnetic fields produced by the orbital motions of the electrons in an atom. Each electron in an atom can be regarded as having some "orbital" motion about the nucleus, and this moving charge represents an electric current, which sets up a magnetic field for the atom, as shown below.

THE PHISICS AROUND

THE PHISICS AROUND

Many atoms have essentially no net magnetic dipole field, because the electrons orbit the nucleus about different axes, so their fields cancel out. Thus, whether or not an atom has a net dipole field depends on the structure of the electron shells surrounding the nucleus. In broad terms, diamagnetism and paramagnetism are different types of responses to an externally applied magnetic field. Diamagnetism is a natural consequence of Lenz's law, according to which the electric current resulting from an applied field will be in the direction that opposes the applied field. . In other words, the induced current will flow in the direction that creates a field opposite to the applied field, as illustrated below

THE PHISICS AROUND

Conservation of energy implies that a force is required to push the magnet through the ring, thereby setting up the flow of current (in the opposite direction of the electron motion). Hence there is a repulsive force between the magnet and the conducting ring. Likewise when an atom is subjected to an applied magnetic field, there is a tendency for the orbital motions of the electrons to change so as to oppose the field.

As a result, the atom is repelled from any magnetic field. Notice that this is true regardless of the polarity of the applied field, because the induced "currents" (i.e., the induced changes in the orbital motions of the electrons) invariably act to oppose the applied field. This phenomenon is present in all substances to some degree, but it is typically extremely small, so it is not easily noticed. It is most evident for elements whose atoms have little or no net magnetic moment (absent an externally applied field). Among all the elements at ordinary room temperatures, bismuth has the strongest diamagnetism, but even for bismuth the effect is extremely weak, because the currents that can be established by the electron orbital motions are quite small. It's possible, however, to construct a perfect diamagnet using superconductivity.

THE PHISICS AROUND

A superconductor is, in many respects, like a quantum-mechanical atom, but on a macroscopic scale, and it can support very large currents. In accord with Lenz's Law, these currents oppose any applied field, so it's actually possible to achieve stable levitation of a permanent magnet over a superconductor. In view of Lenz's Law, it might seem surprising that any material could actually be attracted to a magnetic field, but in fact there are many such substances. This is due to the phenomena called paramagnetism. Unlike the atoms of diamagnetic materials, the electrons of atoms in paramagnetic materials are arranged in such a way that there is a net magnetic dipole due to the orbital motions of the electrons around the nucleus. Thus, each atom is a small permanent magnet, but the poles tend to be oriented randomly, so a macroscopic sample of the substance usually has no net magnetic field.

THE PHISICS AROUND

When such a substance is subjected to an external magnetic field, there is (as always) a small diamagnetic effect on the orbital motions of the electrons, tending to cause a repulsion (as explained above), but there is also a tendency for the individual atomic dipoles to become aligned with the imposed field, rather than being oriented randomly. This gives the substance an overall net magnetic dipole in the same direction as the applied field, so if the substance is located in a non-uniform magnetic field, it will be attracted in the direction of increasing field strength. This paramagnetic attraction effect is much stronger than the diamagnetic repulsion, so paramagnetism usually masks the effect of diamagnetism for such substances. However, even paramagnetism is so weak that it's often not noticed, because the thermal agitation of the atoms (at room temperature) tends to disrupt the alignment.

THE PHISICS AROUND

The last major category of magnetic behavior is called ferromagnetism. This is the phenomenon responsible for the strong magnetic properties of iron, and for the existence of permanent magnets, i.e., macroscopic substances (such as magnetite) that exhibit an overall net magnetic dipole field, even in the absence of any externally applied field. Many of the early researchers in the science of magnetism thought this was nothing but a strong and persistent form of paramagnetism, but the strength and persistence of ferromagnetism show that it is the result of a fundamentally different mechanism, an effect that is absent in merely paramagnetic substances Whereas both diamagnetism and paramagnetism are essentially due to the atomic fields resulting from the orbital motions of the electrons about the nucleus, ferromagnetism is due almost entirely to alignment of the intrinsic spin axes of the individual electrons.

THE PHISICS AROUND

An individual electron possesses a quantum property known as "spin", which is somewhat analogous to the spin of a macroscopic object. (This analogy is not exact, and can be misleading in some circumstances, but it's useful for gaining an intuitive understanding of the magnetic properties of materials.) According to this view, an electron's charge is distributed around its surface, and the surface is spinning about some axis, so there is a tiny current loop, setting up a magnetic field as illustrated below.

THE PHISICS AROUND

The contribution of the nucleus itself to the magnetic field of an atom is typically negligible compared with that of the electrons. In most elements the spin axes of the electrons point in all different directions, so there is no significant net magnetic dipole. However, in ferromagnetic substances, the intrinsic spins of many of the electrons are aligned, both within atoms and between atoms. The key question is what causes all these dipoles to be aligned, especially in the absence of an external field. It can be shown that the dipole interaction itself is not nearly strong enough to achieve and maintain alignment of the electron spin axes at room temperatures, so some other factor must be at work.

THE PHISICS AROUND

Quantum mechanics furnishes the explanation: For particular arrangements of certain kinds of atoms in the lattice structure of certain solids, the inter-electron distances within atoms and between neighboring atoms are small enough that the wave functions of the electrons overlap significantly. As a result, there is a very strong effective "coupling force" between them due to their indistinguishability. This is called an "exchange interaction", and is purely a quantum-mechanical phenomenon. There is no classical analogy. In essence, quantum mechanics tells us that there is a propensity for the identities of neighboring electrons to be exchanged, and this locks the spin orientations of the electrons together.

THE PHISICS AROUND

(This is actually true only under certain circumstances. It's also possible for exchange interactions to lock the spins of neighboring electrons in opposite directions, in which case the behavior is called anti-ferromagnetism.) In order for the exchange interaction to operate, the inter-electron distances must be just right, and these distances are obviously affected by the temperature, so there is a certain temperature, called the Curie temperature, above which ferromagnetism breaks down. Only five elements have electron shell structures that support ferromagnetism, namely, iron, cobalt, nickel, gadolinium, and dysprosium. In addition, many compounds based on these elements are also ferromagnetic. (One example is the compound Fe3O4, also called lodestone, which the ancient Greeks found lying around in Magnesia.) These are all "transition elements", with partially populated 3d inner electron shells.

THE PHISICS AROUND

When magnetized, the spin axes of all the electrons in the 3d shells are aligned, not only for one atom, but for neighboring atoms as well. This gives the overall lattice of atoms a very strong net magnetic dipole. It's worth noting that this is due to the intrinsic spins of the individual electrons, not due to the orbital motions of the electrons (as is the case with diamagnetism and paramagnetism). Recall that, for paramagnetic substances, the alignment of atomic dipoles is maintained only as long as the external field is applied. As soon as the field is removed, the atomic dipoles tend to slip back into random orientations. This is because the ordinary dipole field is not nearly strong enough to resist thermal agitation at room temperatures. In contrast, after a ferromagnetic substance has been magnetized, and the externally applied field is removed, a significant amount of magnetization remains.

THE PHISICS AROUND

THE PHISICS AROUND

In general, the electron spins of all the atoms with a suitable lattice will be locked in alignment, with or without an external field, but a real large-scale piece of a substance typically cannot be a single perfectly coherent lattice. Instead, it consists of many small regions of pure lattices, within which the exchange interaction keeps all the electron spins aligned, but the exchange interaction does not extend across the boundaries between domains. In effect, these boundaries are imperfections in the lattice. As a result, although each small domain is perfectly magnetized, the domains in an ordinary piece of iron are not aligned, so it has no significant net magnetic field. However, when subjected to an external field, there is enough extra impetus to trigger a chain reaction of alignment across the boundaries of the individual regions in the iron, causing the overall object to become a magnet.

THE PHISICS AROUND

This is the phenomenon described by Socrates, when he explained how a Magnet has the power not only to attract iron, but to convey that power to the iron. He was describing a purely quantum mechanical effect, by which an applied magnetic field causes the intrinsic spin axes of individual electrons in the 3d shells of transition elements such as iron to become aligned - although he presumably wasn't thinking about it in those terms. When the external field is removed, the various regions in the iron object will tend to slip back to their natural orientations, given the imperfections in the lattice structure, so much of magnetism of the object will be lost. However, there will be typically have been some structural re-organization of the lattice (depending on the strength of the applied field, and the temperature of the iron), so that a higher percentage of the domains are aligned, and this re-structuring of the lattice persists even after the external field is removed.

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This accounts for the hysteresis effect, by which a piece of iron acquires some permanent magnetism after having been exposed to a strong field. In order to create a strong permanent magnet, a piece of ferrous material is heated to a molten state, and then placed in a strong magnetic field and allowed to cool. This creates a lattice structure with very few magnetic imperfections in the lattice, so the electron spins are naturally locked in alignment throughout the material. Not surprisingly, if a magnetized piece of iron is struck with a hammer, it's possible to scramble the domains and thereby de-magnetize the object In summary, the three main kinds a magnetism are illustrated schematically in the figures below.

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2) GyroscopeThe gyroscope is an instrument that allows to verify immediately that an object placed in spin stretches to conserve the direction of the spin axis. The force necessary to move the direction of the spin axis is as greater as the rotation spin speed is. This means that an object place in very fast spin keeps the direction of its spin axis costant. On this principle very sophisticated devices are based in the guide of the airplanes that make satellite navigation systems work. You can find them in the most expensive cars. Also the possibility to be in equilibrium on a bicycle is tied partially to the speed of spin of the wheels that stretch to maintain to horizontal their spin axis and therefore contrasts the tendency of the bicycle to falling on a side.

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“Gyroscope” used in satellite navigation systems

In satellite navigation systems it is essential to know the position of the automobile. The gyroscope is used in this case to know the value of the angular movement (rotations) made by vehicle. The gyroscope installed on the navigation system, generally settled on the back of the automobile is a sensor of piezoelectric angular velocity (Rate Gyro). So it’s a sensible sensor to rotation angular velocity that through integration in time gives information about the angular movement (degrees) made by the car.

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Functioning:The “heart” of the device is a ceramics bar line that flutes around his longitudinal axis. The bar line is suspended on two metallic axis with two welding points settled on the oscillation junctions of the bar line. If the bar line rolls, it originates the Coriolis force on the normal level to the one of oscillation, proportional to the angular velocity. The piezoelectric platens applied on the bar line are useful to vibrate the bar line lengthwise and to eliminate the vibration on the normal level, originated by Coriolis force. The essential tension to eliminate the vibration on the normal level gives information about the speed of the rotation of bar line (so the gyroscope). So the gyroscope generates an exit tension proportional to the angular velocity to which it’s submitted.

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The Artificial Horizon:The Artificial Horizon is the pointer of order generally employed on the simpler airplanes. The spin axis is constituted by a gyroscope to three degrees of freedom, having vertically disposed, and therefore the disc place in spin in the horizontal plan. In agreement to gyroscope there is a line or a representation of the horizon, that is therefore always parallel to the horizon, while in agreement to the case of the instrument is a shape that represents the airplane, which can be rised or lowered on the horizon through an appropriate revolving knurl. Making the shape coincide with the line of the horizon when the airplane is on the line of flight, the assumed orders can be visualized around to the bank axis and around to its pitch.

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The picture shows five flight attitudes indicated by an artificial horizon:

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TWO CURIOUS PHISYCAL EXPERIENCES:Seats and gyroscope:seated over a revolving seat,we support a bycicle wheel,with an horizontal axis(the wheel has two handles)if the wheel is put in spin,and we tilt the axis of the wheel,we also begin to turn.

Suspended wheel:a bycicle wheel with an axis, an extremity of which is suspended to the ceiling trough a rope,it is kept to turning with the horizontal axis and,after that,is released.What does the wheel do? Contrarily at what we think,the wheel maintains its horizontal axis until the speed of the spin is quite high.

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SHORT HISTORY OF THE BICYCLEThe origins of the bicycle are debatables.In 1796,a “celerifero” ,vehicle equipped of two wheels on the same vertical axis, was assembled.The wheels were linked by a small beam (not yet equipped of a seat) astride of which they moved thanks to the push gave from the feet .Some years after,the German Drais inserted two remarkable varyings:a saddleback to sit and a handle-bar to ride the mean.

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DRAISINA (1820)The “celerifero”,and later “velocifero”, was constituted by a wooden rigid chassis with two wheels on which the rider stood astride,pulling the mean with his feet. The Bavarian baron Carl von Drais,in 1818,modified his own “velocifero” equipping it with a handle-bar to direct the anterior wheel,making easier the use and the maneuver. This mean was called “Draisino” and it can be considered as a precursor of the current bicycles. The “Draisina” represented an enormous progress about “celeriferi” which,in fact,could not steer and, therefore, face curves.

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MICHAUX PENNY-FARTHING (1869)With the application of the stocks on the front wheel born the “michaudine”.The name of these velocipedi comes from French mechanics Piero & Ernesto Michaux(father and son).

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DRAISINA WITH LEVERS:

TECHNICAL DESCRIPTION:A draisina with levers,stocks and connecting rods;only lever for steering-gear and brake;

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PENNY-FARTHING LALLEMENT

TECHNICAL DESCRIPTION:Pedals introduction on a loom like “draisina”; Hanged saddle elastically;steering and pedals to the drive wheel;elegant shape of the support crosspiece.

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PENNY-FARTHING ENGLISH MODEL

TECHNICAL DESCRIPTION:Hanged saddle elastically;Recordable pedals;Sliding block brake on the posterior wheel.

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TRICYCLE MURNIGOTTI (1879)

TECHNICAL DESCRIPTION: First application of the motor to the tricycle; to hydrogen engine; two cylinders.

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KANGOROO(1880)

Marseillaise Rousseau decided to apply two gears with transmission to chain in order to increase the speed, and he realized it in 1878. Later on, in order to distinguish from the other exemplaries, it was called “Kangoroo”.In order to avoid the turn over of the runner, typical of the bicycles with two wheels of great diameter, the use of the chain with multiplies is introduced in order to contain the diameter of the front wheel and to maintain a high speed in means.

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MONOCYCLE (1882)

TECHNICAL DESCRIPTION:Iron chassis;Iron wheel with radial and driven in beams.

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CADRE BI-CYCLE (1885)

TECHNICAL DESCRIPTION:Front stirrups for rest;Posterior stirrups for climb in race;Humber chain;Recordable pedals.

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BICYCLE (1893)

TECHNICAL DESCRIPTION:Ice-skate brake on the front wheel;French “galle” chain;Pneumatic rubbers

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3) The Earnshaw theorem

One of the most common questions about permanent magnets is whether there exist a stable and static configuration of permanent magnets that will cause an object to be levitated indefinitely. Obviously the levitation itself is not a problem, because many magnets have fields strong enough to lift their own weight. Equilibrium is also not a problem, because there is obviously a configuration at the boundary between falling and rising. The problem is stability. In order to have stability, there must be a restorative force counter-acting any displacement away from the equilibrium point. We need to be careful when considering this question, because, as discussed above, there are several kinds of magnetic behavior exhibited by different substances in different circumstances. We can certainly achieve stable levitation with a superconductor, which is really just a perfect diamagnet.

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In fact, even at room temperatures, it is possible to use the diamagnetic property of a substance like bismuth to achieve (marginal) stability for magnetic levitation. Of course, in such a case, the paramagnet is too weak to do the actual levitating; it just provides a small window of stability for an object that is actually being lifted by ferromagnetic effects. But if we set aside the phenomenon of paramagnetism, which is a constantly self-adjusting field, and focus strictly on fixed fields as are produced by ferromagnets, can we achieve stable static levitation? In 1842, Samuel Earnshaw proved what is now called Earnshaw's Theorem, which states that there is no stable and static configuration of levitating permanent magnets. (See Earnshaw, S., On the nature of the molecular forces which regulate the constitution of the luminiferous ether., 1842, Trans. Camb. Phil. Soc., 7, pp 97-112.)

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The term "permanent magnet" is meant to specify ferromagnetism, which is truly a fixed magnetic field relative to the magnet. In contrast, the phenomena of diamagnetism is not really "permanent", both because it requires the presence of an externally applied field, and more importantly (from the standpoint of Earnshaw's theorem) because the diamagnetic field constantly adapts to changes in the applied external field. This is why stable diamagnet levitation (of which superconductors provide the extreme example) is possible, in spite of Earnshaw's theorem. It's worth noting that Earnshaw's theorem - ruling out the possibility of static stable levitation - presented scientists at the time with something of a puzzle, if not an outright paradox, because we observe stable configurations of levitating objects every day.

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For example, the book sitting on my desk is being levitated, and some force is responsible for this levitation. Admittedly it may not have been clear in Earnshaw's day that the book's interaction with the desk was via electromagnetic forces, but Earnshaw's theorem actually applies to any classical particle-based inverse-square force or combination of such forces. Since we observe stable levitation (not to mention stable atoms and stable electrons), it follows from Earnshaw's theorem that there must be something else going on, viz., we cannot account for the stable structures we observe in nature purely in terms of classical inverse-square forces, or even in terms of any kind of classical conservative forces. In order to explain why stable atoms are possible (i.e., why the electrons don't simply spiral in and collide with the protons) and why other stable structures are possible, it's necessary to invoke some other principle(s). Something like quantum mechanics and the exclusion principle is required.

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The proof of Earnshaw's theorem follows closely from Gauss's law. Indeed this accounts for the generality of its applicability. To consider the simplest case, suppose we wish to arrange a set of charged particles in such a way that a region of stable containment for an electron is established. This requires the existence of a point in empty space such that the force vector everywhere on the surface of an incremental region surrounding that point is directed inward. But according to Gauss's law, the integral of the force vector over any closed surface equals the charge contained within the surface. Thus the integral of the force over any closed surface in empty space is zero, which implies that if it points inward on some parts of the surface, it must point outward on other parts, so it is clearly not a stable equilibrium point. The best we could do is have a force of zero over the entire surface, but this too is not stable, because there is no restorative force to oppose any perturbations.

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According to Gauss' law, the only point that could possibly be a stable equilibrium point for an electron is a point where a positive charge resides, e.g., a proton. Classically an electron would be expected to collapse onto a proton, assuming it had no angular momentum. In the presence of angular momentum, it's possible to have (idealized) stable orbits in the context of Newtonian gravitation, because Newton's gravity did not radiate energy when charges (i.e., masses) are accelerated. However, electric charges were known classically to radiate energy, so even naive orbital models were ruled out. This made it clear that some other principles must be invoked to account for stable configurations of electrically charged matter. (In general relativity, simple two-body orbital systems also radiate energy, in the form of gravitational waves, so the same argument can ultimately be against the possibility of stable configurations for inertially charged matter as well, although in this case the rate of energy radiation is so low that the configurations are essentially stable for practical purposes.)

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Incidentally, if we don't require a static configuration, then it is possible to achieve quasi-stable levitation with permanent magnets by spinning the levitated object and using the gyroscopic moments to offset the instability. A number of interesting devices of this type have been constructed. This form of levitation is called quasi-stable (rather than stable) because the rotation of the levitating object results in the emission of energy in the form of electromagnetic waves, so eventually the rotation will be brought to a stop, and then the system will go unstable.

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Maglev train

Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles via electromagnetic force. This method can be faster than wheeled mass transit systems, potentially reaching velocities comparable to turboprop and jet aircraft (500 to 580 km/h). The world's first commercial application of a high-speed maglev line is the IOS (initial operating segment) demonstration line in Shanghai, China that transports people 30 km (18.6 miles) to the airport in just 7 minutes 20 seconds (top speed of 431 km/h or 268 mph, average speed 250 km/h or 150 mph). Other maglev projects worldwide are being studied for feasibility. However, scientific, economic and political barriers and limitations have hindered the widespread adoption of the technology.

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All operational implementations of maglev technology have had minimal overlap with wheeled train technology and have not been compatible with conventional railroad tracks. Because they cannot share existing infrastructure, maglevs must be designed as complete transportation systems. The term "maglev" refers not only to the vehicles, but to the railway system as well, specifically designed for magnetic levitation and propulsion.

Technology:See also fundamental technology elements in the JR-Maglev article, Technology in the Transrapid article, Magnetic levitation

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There are two primary types of maglev technology:•electromagnetic suspension (EMS) uses the attractive magnetic force of a magnet beneath a rail to lift the train up. •electrodynamic suspension (EDS) uses a repulsive force between two magnetic fields to push the train away from the rail.

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Electromagnetic suspension:In current EMS systems, the train levitates above a steel rail while electromagnets, attached to the train, are oriented toward the rail from below. The electromagnets use feedback control to maintain a train at a constant distance from the track.

Electrodynamic suspension:

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EDS Maglev Propulsion via propulsion coils:

In Electrodynamic suspension (EDS), both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. The magnetic field in the train is produced by either electromagnets (as in JR-Maglev) or by an array of permanent magnets (as in Inductrack). The repulsive force in the track is created by an induced magnetic field in wires or other conducting strips in the track.At slow speeds, the current induced in these coils and the resultant magnetic flux is not large enough to support the weight of the train. For this reason the train must have wheels or some other form of landing gear to support the train until it reaches a speed that can sustain levitation.

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Propulsion coils on the guideway are used to exert a force on the magnets in the train and make the train move forwards. The propulsion coils that exert a force on the train are effectively a linear motor: An alternating current flowing through the coils generates a continuously varying magnetic field that moves forward along the track. The frequency of the alternating current is synchronized to match the speed of the train. The offset between the field exerted by magnets on the train and the applied field create a force moving the train forward.

Pros and cons of different technologies:Each implementation of the magnetic levitation principle for train-type travel involves advantages and disadvantages. Time will tell as to which principle, and whose implementation, wins out commercially.

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Technology   Pros   ConsEMS Electromagnetic Magnetic fields inside and outside the

vehicle are insignificant; proven, commercially available technology that can attain very high speeds (500 km/h); no wheels or secondary propulsion system needed

Electromagnetic EDS

Electrodynamic

The separation between the vehicle and the guideway must be constantly monitored and corrected by computer systems to avoid collision due to the unstable nature of electromagnetic attraction.

Onboard magnets and large margin between rail and train enable highest recorded train speeds (581 km/h) and heavy load capacity; has recently demonstrated (Dec 2005) successful operations using high temperature superconductors in its onboard magnets, cooled with inexpensive liquid nitrogen

Strong magnetic fields onboard the train would make the train inaccessible to passengers with pacemakers or magnetic data storage media such as hard drives and credit cards, necessitating the use of magnetic shielding; vehicle must be wheeled for travel at low speeds; system per mile cost still considered prohibitive; the system is not yet out of prototype phase.Inductrack System

(Permanent Magnet EDS)

Failsafe Suspension - no power required to activate magnets; Magnetic field is localized below the car; can generate enough force at low speeds to levitate maglev train; in case of power failure cars slow down on their own in a safe, steady and predictable manner before coming to a stop; Halbach arrays of permanent magnets may prove more cost-effective than electromagnets

Requires either wheels or track segments that move for when the vehicle is stopped. New technology that is still under development (as of 2007) and has as yet no commercial version or full scale system prototype.

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Neither Inductrack nor the Superconducting EDS are able to levitate vehicles at a standstill, although Inductrack provides levitation down to a much lower speed. Wheels are required for both systems. EMS systems are wheel-less.

The German Transrapid, Japanese HSST (Linimo), and Korean Rotem EMS maglevs levitate at a standstill, with electricity extracted from guideway using power rails for the latter two, and wirelessly for Transrapid. If guideway power is lost on the move, the Transrapid is still able to generate levitation down to 10 km/h speed, using the power from onboard batteries. This is not the case with the HSST and Rotem systems.

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Propulsion:An EMS system can provide both levitation and propulsion using an onboard linear motor. EDS systems can only levitate the train using the magnets onboard, not propel it forward. As such, vehicles need some other technology for propulsion. A linear motor (propulsion coils) mounted in the track is one solution. Over long distances where the cost of propulsion coils could be prohibitive, a propeller or jet engine could be used.

Stability:Static magnetic bearings using only electromagnets and permagnets are unstable, as explained by Earnshaw's theorem. EMS systems rely on active electronic stabilization. Such systems constantly measure the bearing distance and adjust the electromagnet current accordingly. As all EDS systems are moving systems (i.e. no EDS system can levitate the train unless it is in motion), Earnshaw's theorem does not apply to them.

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Pros and cons of maglev vs. conventional trains:Due to the lack of physical contact between the track and the vehicle, there is no rolling friction, leaving only air resistance (although maglev trains also experience electromagnetic drag, this is relatively small at high speeds).Maglevs can handle high volumes of passengers per hour (comparable to airports or eight-lane highways) and do it without introducing air pollution along the right of way. Of course, the electricity has to be generated somewhere, so the overall environmental impact of a maglev system is dependent on the nature of the grid power source.The weight of the large electromagnets in EMS and EDS designs are a major design issue. A very strong magnetic field is required to levitate a massive train. For this reason one research path is using superconductors to improve the efficiency of the electromagnets.Due to its high speed and shape, the noise generated by a maglev train is similar to a jet aircraft, and is considerably more disturbing than standard steel on steel intercity train noise. A study found the difference between disturbance levels of maglev and traditional trains to be 5dB (about 78% noisier).

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Economics:The Shanghai maglev cost 9.93 billion yuan (US$1.2 billion) to build.This total includes infrastructure capital costs such as manufacturing and construction facilities, and operational training. At 50 yuan per passenger and the current 7,000 passengers per day, income from the system is incapable of recouping the capital costs (including interest on financing) over the expected lifetime of the system, even ignoring operating costs.China aims to limit the cost of future construction extending the maglev line to approximately 200 million yuan (US$24.6 million) per kilometer. These costs compare competitively with airport construction (e.g., Hong Kong Airport cost US$20 billion to build in 1998) and eight-lane Interstate highway systems that cost around US$50 million per mile in the US.While high-speed maglevs are expensive to build, they are less expensive to operate and maintain than traditional high-speed trains, planes or intercity buses. Data from the Shanghai maglev project indicates that operation and maintenance costs are covered by the current relatively low volume of 7,000 passengers per day.

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Passenger volumes on the Pudong International Airport line are expected to rise dramatically once the line is extended from Longyang Road metro station all the way to Shanghai's downtown train depot.The proposed Chūō Shinkansen line is estimated to cost approximately US$82 billion to build.The only low-speed maglev (100 km/h) currently operational, the Japanese Linimo HSST, cost approximately US$100 million/km to build. Besides offering improved O&M costs over other transit systems, these low-speed maglevs provide ultra-high levels of operational reliability and introduce little noise and zero air pollution into dense urban settings.As maglev systems are deployed around the world, experts expect construction costs to drop as new construction methods are perfected.

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