Transcript Document 7169535

SORA
CLASSES: IV
Sez. A-B
TEACHERS:
ANNARITA SBARDELLA
EMILIANA MANCINI
VINCENZO 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 – ITALY
COMENIUS 1.3
“ENCOHAN - ENERGY IN THE CONSUMERS’ HANDS”
2005 - 2008
CLASSES: IV Sez. A-B
TEACHERS:
ANNARITA SBARDELLA
EMILIANA MANCINI
VINCENZO RECCHIA
LICEO SCIENTIFICO STATALE "LEONARDO DA VINCI" SORA – ITALY
COMENIUS 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 BIRD
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
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.
DRINKING BIRD
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.
THE PHISICS AROUND :
1) Heat engine
A 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 :
Figure 1: Heat engine diagram
Heat 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 (4stroke/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.
THE PHISICS AROUND :
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:
Thermodynamic cycles:
Figure 1: Heat engine diagram
Atkinson cycle
Brayton/Joule cycle
Carnot 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
THE PHISICS AROUND
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:
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.
Water condenses into visible
droplets after evaporating from
a cup of hot tea
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
CONDENSATION OF WATER IN NATURE:
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.
Dew on a spider web
THE PHISICS AROUND
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.
Condensation on a
cold bottle of water
THE PHISICS AROUND
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.
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.
THE PHISICS AROUND
3) Ideal gas law
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 [m3 ]
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 PHISICS AROUND
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 forms
Considering 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,
and since ρ = m / V, we find that the ideal gas law can be re-written as:
THE PHISICS AROUND
PROOF:
Empirical
The 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
If it then undergoes an isothermal process:
Where:
p = final pressure
v = final volume
T = final temperature (= t')
So:
THE PHISICS AROUND
Where:
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:
THE PHISICS AROUND
Theoretical
The 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.
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.
LEVITRON
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 electromagnetic 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.
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
THE PHISICS AROUND
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 electroheraclian 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 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 PHISICS AROUND
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
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.
THE PHISICS AROUND
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
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 restructuring of the lattice persists even after the external field is
removed.
THE PHISICS AROUND
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 demagnetize the object In summary, the three main kinds a magnetism are
illustrated schematically in the figures below.
THE PHISICS AROUND
2) Gyroscope
The 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.
THE PHISICS AROUND
“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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
The picture shows five flight attitudes indicated by an artificial horizon:
THE PHISICS AROUND
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.
THE PHISICS AROUND
SHORT HISTORY OF THE BICYCLE
The 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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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).
THE PHISICS AROUND
DRAISINA WITH LEVERS:
TECHNICAL DESCRIPTION:
A draisina with levers,stocks and connecting rods;only lever
for steering-gear and brake;
THE PHISICS AROUND
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.
THE PHISICS AROUND
PENNY-FARTHING ENGLISH MODEL
TECHNICAL DESCRIPTION:
Hanged saddle elastically;
Recordable pedals;
Sliding block brake on the posterior wheel.
THE PHISICS AROUND
TRICYCLE MURNIGOTTI (1879)
TECHNICAL DESCRIPTION:
First application of the motor to the tricycle; to hydrogen engine; two cylinders.
THE PHISICS AROUND
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.
THE PHISICS AROUND
MONOCYCLE (1882)
TECHNICAL DESCRIPTION:
Iron chassis;
Iron wheel with radial and driven in beams.
THE PHISICS AROUND
CADRE BI-CYCLE (1885)
TECHNICAL DESCRIPTION:
Front stirrups for rest;
Posterior stirrups for climb in race;
Humber chain;
Recordable pedals.
THE PHISICS AROUND
BICYCLE (1893)
TECHNICAL DESCRIPTION:
Ice-skate brake on the front wheel;
French “galle” chain;
Pneumatic rubbers
THE PHISICS AROUND
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 counteracting 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.
THE PHISICS AROUND
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 selfadjusting 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.)
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.)
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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
THE PHISICS AROUND
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.
THE PHISICS AROUND
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:
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
Technology
EMS Electromagnetic
Electromagnetic EDS
Electrodynamic
Inductrack System
(Permanent Magnet
EDS)
Pros
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
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
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
Cons
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.
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.
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
THE PHISICS AROUND
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).
THE PHISICS AROUND
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.
THE PHISICS AROUND
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.
• END