E-cat patent

METHOD AND APPARATUS FOR CARRYING OUT NICKEL AND HYDROGEN EXOTHERMAL REACTIONS
http://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=2009125444&KC=&FT=E&locale=en_EP
http://www.wipo.int/pctdb/en/wo.jsp?IA=IT2008000532&DISPLAY=DESC

E-cat by Rossi&Focardi

"he Energy Catalyzer (sometimes shortened to E-Cat) is an apparatus built by inventor Andrea Rossi, with support from his scientific consultant, physicist and emeritus professor Sergio Focardi. The 2009 patent application claims "a method and apparatus for carrying out nickel and hydrogen exothermal reactions," with production of copper. Although the patent cites previous works on cold fusion, one statement by Rossi asserted that it is not cold fusion, but rather LENR, Low-Energy Nuclear Reaction. A similar system, but yielding considerably less power, had previously been described by Focardi et al."
Read
http://en.wikipedia.org/wiki/Energy_Catalyzer

Ny Teknik tested the energy catalyzer - NyTeknik

"The energy catalyzer was demonstrated publicly for first time on the 14th January 2011. According to its inventor Andrea Rossi it has a closed reactor of steel that is loaded with nickel powder plus secret catalysts and pressurized with hydrogen."

Ny Teknik tested the energy catalyzer - NyTeknik

GRACE

The Gravity Recovery And Climate Experiment (GRACE), a joint mission of NASA and the German Space Agency, has been making detailed measurements of Earth's gravity field since its launch in March 2002.

Gravity is determined by mass. By measuring gravity, GRACE shows how mass is distributed around the planet and how it varies over time. 

GRACE is a collaborative endeavor involving the Center for Space Research at the University of Texas, Austin; NASA's Jet Propulsion Laboratory, Pasadena, Calif.; the German Space Agency and Germany's National Research Center for Geosciences, Potsdam. The Jet Propulsion Laboratory is responsible for the overall mission management under the NASA ESSP program.

http://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_Experiment

Tuning neurons

"Have you ever wondered why certain sets of musical notes sound perfectly melodious while others make you want to cover your ears? Now, physicists in Europe have developed a model that suggests that certain notes sound harmonious because of the consistent rhythmic firing of neurons in the auditory system."

Physicists in tune with neurons - physicsworld.com

Magnetic scan without magnet

Magnetic scans with a tiny magnet, by Michael Schirber, a discussion of the paper entitled Near-Zero-Field Nuclear Magnetic Resonance by M. P. Ledbetter, T. Theis, J. W. Blanchard, H. Ring, P. Ganssle, S. Appelt, B. Blümich, A. Pines, and D. BudkerPhys. Rev. Lett. 107, 107601 (Published September 1, 2011)
"Nuclear magnetic resonance is a powerful technique for analyzing molecular structure in biology, medicine, and materials science. Conventionally, it calls for huge magnets to align nuclear spins and to detect them with high sensitivity, but recent work has demonstrated that similar analysis can be done without a magnetic field. The problem with this zero-field technique is that it can’t unambiguously identify molecules. Now, in a paper in Physical Review Letters, Micah Ledbetter of the University of California, Berkeley, and his collaborators address this limitation, showing that a very small magnetic field can provide extra signatures for chemical discrimination."
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.107.107601

Collision may have shaped the Moon

"Differences between the near and far sides of the Moon could be the result of a collision between the Moon and a "Trojan" companion that occurred billions of years ago. That is the conclusion of geophysicists in the US and Switzerland who have done computer simulations on how the Moon would be affected by such a massive impact."

Trojan collision may have shaped the Moon - physicsworld.com

Flowing water may exist on Mars

"Liquid water might exist on Mars today, according to a group of scientists in the US. Images from NASA's Mars Reconnaissance Orbiter (MRO) reveal that dark, narrow, finger-like structures follow slopes in certain regions of the southern hemisphere of the planet during its summer months."

Flowing water may exist on Mars - physicsworld.com

Spinons

"An international group of researchers has measured, for the first time, the phenomenon of spin–charge separation in bulk in a solid. They also found that the material violates the empirical Wiedemann–Franz law that has held true for more than 150 years."

Spinons take the heat - physicsworld.com

In fact, it is well kwown that the Wiedermann-Franz law is an approximation.

Artificial leaves make fuel

"Two teams of researchers in the US have taken important steps towards the creation of commercially viable "artificial leaf" – a hypothetical device that can turn sunlight into electrical energy or fuel by mimicking some aspects of photosynthesis.

Earlier this year, the chemist Daniel Nocera at the Massachusetts Institute of Technology (MIT) announced artificial-leaf prototypes at the annual meeting of the American Chemical Society in California. Now, working with two different teams of researchers, he has published two papers on different devices that represent progress towards effective and commercially viable versions of the artificial leaf."

Artificial leaves make fuel from sunlight - physicsworld.com

Shoemaker (formerly Teague) Impact Structure

"The Shoemaker (formerly Teague) Impact Structure—located in Western Australia in a drainage basin south of the Waldburg Range—presents an other-worldly appearance in this astronaut photograph. The Shoemaker impact site is approximately 30 kilometers (19 miles) in diameter and clearly defined by concentric ring structures formed in sedimentary rocks (brown to dark brown, image center). The rocks were deformed by the impact event approximately 1.63 billion years ago (as reported by the Earth Impact Database). Other age-dating analyses of granitic rocks at the core of the structure call this age into question (Pirajno et al. 2003)."
http://eol.jsc.nasa.gov/EarthObservatory/Shoemaker_Impact_Structure.htm
"Beginning with the Mercury missions in the early 1960s, astronauts have taken photographs of the Earth. Our database tracks the locations, supporting data, and digital images for these photographs. We process images coming down from the International Space Station on a daily basis and add them to the 1,101,059 views of the Earth already made accessible on our website."

Biofuel for flights

"Lufthansa, Europe's second-largest airline, became the first carrier in the world to offer regular scheduled flights running on biofuel, with four daily round trips between Hamburg and Frankfurt.
The airline will use a biofuel blend using 50 per cent so- called hydrotreated renewable jet fuel, Lufthansa said. The fuel is made from feedstocks including inedible plants and wood chips. Lufthansa will fly an Airbus A321 on the services." Read more
http://www.smh.com.au/travel/travel-news/lufthansa-begins-worlds-first-regular-biofuel-flights-20110718-1hks1.html

La portata

Testo e immagini adattate da 

Halliday Resnick Walker

Fondamenti di Fisica

Millikan's experiment

Testo e immagine adattati da

Halliday - Resnick - Crane

Fisica II

Dipolo

Un dipolo elettrico è un sistema composto da due cariche elettriche uguali e opposte di segno. È uno dei più semplici sistemi di cariche che si possano studiare e rappresenta inoltre l'approssimazione basilare del campo generato da un insieme di cariche globalmente neutro tramite lo sviluppo in multipoli di quest'ultimo.

Immagini adattate dal libro

Halliday, Resnick, Krane, Fisica 2

n.14 - Esercizio - elettrostatica

Volcanoes under Antarctic waters

"Scientists from British Antarctic Survey (BAS) have discovered previously unknown volcanoes in the ocean waters around the remote South Sandwich Islands. Using ship-borne sea-floor mapping technology during research cruises onboard the RRS James Clark Ross, the scientists found 12 volcanoes beneath the sea surface — some up to 3km high. They found 5km diameter craters left by collapsing volcanoes and 7 active volcanoes visible above the sea as a chain of islands."
More http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=1541

An acoustic superlens from a few cans of cola

""Acoustic metamaterial" may sound exotic, but researchers in France have managed to assemble one from a few multipacks of cola cans. Arranged in a grid, the drinks cans act as a superlens for sound, focusing acoustic waves into much smaller regions than their metre-long wavelengths typically allow. The cans act as resonators, directing the volume of the sound to peak in a space just a few centimetres wide, and this heightened precision could improve acoustic-actuator systems."

How to make a superlens from a few cans of cola - physicsworld.com

n.13 - due piani carichi

Two infinite sheets of  electric charges with uniform densities intersect at right angles. The plane of the figure is perpendicular to the planes. Let us suppose that changes cannot move.
a) Find the magnitude and direction  of the electric field everywhere and sketch the lines of the field, in the case that a sheet has positive density (+sigma) and the other an equal but negative density (-sigma).
b) find the magnitude and direction of the electric  field everywhere and sketch the lines of the field, in the case that the two sheets have the same densitity with the same positive sign, + sigma.
c) Find the difference of potential V(A)-V(B), between the point A and B placed at a distance d on a line in the plane of the figure at 45° with respect to the charged planes.

n.12 - una piccola sfera

n.11 - tre piani

n.10 - due piani

n.9 - tre cariche puntiformi

n.8

DNA transistor

"Passivated nanopores withstand extreme voltages.
Solid-state nanopores are a core element of next-generation single molecule tools in the field of nanobiotechnology, most prominently in the area of DNA-sequencing technology. Researchers at the IBM T. J. Watson Research Center have recently introduced a nanopore-based DNA sequencing platform, which they call a DNA transistor. Thin-film electrodes are integrated into the nanopore device for electrically interacting with translocating DNA. They have now shown that TiN electrodes inside a nanopore can be passivated and completely shielded against electrochemical deterioration even when extreme voltages are applied."

http://nanotechweb.org/cws/article/lab/46476

electrochemical impedance spectroscopy

"Functionalized electrochemical impedance spectroscopy device targets personalized medicine.
Rapid, sensitive, accurate, miniaturized and inexpensive biosensors are highly desirable for assisting clinical medical diagnosis. Researchers based at National Chiao Tung University, Taiwan, have developed such a portable bio-sensing platform to detect intermolecular interactions using nanogold-enhanced electrochemical impedance spectroscopy (EIS)."

http://nanotechweb.org/cws/article/lab/46448
http://iopscience.iop.org/0957-4484/22/24/245105/

Drag the light

"By slowing a beam of light down to the speed of sound, UK researchers have dragged photons by an unprecedented 5°, proving a longstanding theory of physics and opening up potential applications in quantum data storage."
Scientists drag light by 5° by slowing to the speed of sound | News | The Engineer

Pendolo cicloidale

Il pendolo cicloidale è un tipo di moto periodico ideato da Christiaan Huygens intorno al 1659 con una peculiare proprietà: le sue oscillazioni sono isocrone indipendentemente dalla loro ampiezza. Si è visto infatti che questo vale nel caso del pendolo semplice solo per ampiezze abbastanza piccole. Huygens dimostrò invece che un punto materiale che oscilla seguendo una traiettoria cicloidale sotto l'azione della gravità ha un periodo costante che dipende unicamente dalle dimensioni della cicloide.
more  http://it.wikipedia.org/wiki/Pendolo#Pendolo_cicloidale

A far quasar

"A team of European astronomers, including UK astronomers, have discovered a bright quasar that has been beaming light since the Universe was a mere 770 million years old.
The brilliant beacon, named ULAS J1120+0641, is powered by a black hole with a mass two billion times that of the Sun. Located at a redshift – a term relating to astronomical distances – of 7.1, its light has taken 12.9 billion years to reach us. The next most distant quasar is seen at 870 million years after the big bang, or a redshift of 6.4, although gamma ray bursts have been detected at greater distances of 8.6 and 8.2 redshifts."
Most distant quasar shines brightly

Treni

Due treni partono da due stazioni distanti 20 km dirigendosi uno verso l’altro alle rispettive velocità costanti di v1  = 50 km/h  e v2  = 100 km /h. Dopo quanto tempo si incontrano ?

I due treni si incontrano quando sono nello stesso punto allo stesso istante. Oppure quando lo spazio x1 percorso dal primo più lo spazio x2 percorso dal secondo, sommati, danno la distanza totale che separa le due stazioni.

In formule, per il moto uniforme: x1 = v1 t,   x2 = v2 t

All’istante dell’incontro: x1  + x2 = v1 t + v2 t = 20 km

v1 =  50 km/h =   13,89 m/s
v2 = 100 km/h =   27,778 m/s
20 000 m = (13,89m/s) t + (27,778 m/s) t
t = 20 000 / 41,67 s = 480 s

v^2

Un automobilista sta guidando a una velocità costante di 80 km/h quando vede un ostacolo sulla strada a 50 m. I freni gli consentono di sviluppare una decelerazione  a = - 6 m/s^2. Riuscirà il guidatore a fermarsi prima dell'ostacolo?  (s^2 significa s al quadrato)

Il moto é rettilineo uniformemente decelerato, ossia con accelerazione costante negativa. Diciamo S lo spazio di frenata, conosciamo accelerazione, velocità iniziale e velocità finale, che deve essere zero. Utilizziamo l'equazione:

vfin^2 = viniz^2 + 2aS

Trasformiamo la velocità in m/s: viniz = 80 km/h = 22,222 m/s.

L’equazione precedente diventa: 0 = (22,222 m/s)^2 + 2⋅(-6 m/s^2)⋅S

Quindi: S = 41,2 m

L'ostacolo è a 50 metri e quindi l'automobilista si ferma prima.

Cinematica con dinamica

Un oggetto viene lanciato su una rampa inclinata di 45° con una velocità iniziale di 30 m/s. Dopo quanto tempo si ferma ? A che altezza dal suolo arriva?

Sia O l'origine. Il riferimento sia paralleo al piano inclinato verso l'alto. La direzione di moto è  positiva quando è erso l’alto. La velocità iniziale risulta positiva e l’accelerazione di gravità (diretta verso il basso)
negativa.  Valuatiamo la componente dell’accelerazione lungo la direzione di moto, che risulta essere: a = -g sen α = - 6,94 m/s (con g indico il modulo dell'acc. di gravità, pari a 9.8m/s^2).
Per calcolare il tempo che occorre all’oggetto per fermarsi devo ricordarmi che la velocità finale, in
questo caso, é nulla, e poi usare la definizione di accelerazione:

a = (vfin - v iniz)/ t

Nel nostro caso: -g sen α = - 6,94  m/s^2= (vfin - v iniz)/ t= (0 -  30 m/s) / t

Quindi:

t = 4,32 s

Per calcolare lo spazio S percorso sulla rampa, ho a disposizione due espressioni:

S = 1/2 a t^2 + viniz t

Si ottiene:

S = 1/2 (- 6,94) (4,32)^2 + 30 ⋅ 4,32 =  64,8 m

La quota H raggiunta sul livello del suolo la si ricava come:

H = S sen α = 64,8 m ⋅ sen 45° = 45,8 m

Asta

Esercizio sulla Statica dei Corpi Rigidi,  Prof. T.Papa.

Being a red blood cell

"Nanoparticles disguised as red blood cells could be used to deliver anti-cancer drugs directly to a tumour. So say researchers at the University of California at San Diego, whose new technique is unique in its approach to harnessing nanoparticles.

Drug delivery systems that mimic naturally occurring biological molecules seem to be the most efficient when it comes to delivering drugs to tumours. Such systems – usually based on nanoparticles – can also circulate in the body for extended periods of time without being rejected by the body's immune system."

Nanoparticles play at being red blood cells - physicsworld.com

Aircrafts make clouds rain

"For more than 50 years it has been known that aircraft can punch large holes or carve out canals inside clouds as they pass through them – but no-one had been able to explain exactly why this happens. Now researchers in the US have identified the cause by comparing satellite images of clouds with the results of computer modelling. They say that the phenomenon could lead to extra precipitation in the vicinity of major airports."

Aircraft punch holes in clouds and make it rain - physicsworld.com

A "Mobius" graphene

"In 1858, August Mobius dreamt up a shape with a single surface and only one edge. The Mobius strip has fascinated children and scientists alike since then.
How small can these shapes be? In December 2003, German chemists made a molecular Mobius strip out of a benzene-like ring modified with a belt-like carbon structure. Since then, various groups have produced increasingly bizarre Mobius-type molecules, including one that can switch back and forth from a Mobius to an ordinary strip when zapped with light.
Of course, the obvious choice of material with which to make Mobius molecules is graphene. But this particular trick has eluded chemists, an omission that clearly irks. Now Douglas Galvao from the Universidade Estadual de Campinas in Sao Paolo, Brazil, and buddies have decided to grip the bull by the horns and calculated the properties that Mobius carbon might have."New form of "Mobius" carbon predicted - Technology Review

New form of "Mobius" carbon predicted - Technology Review

Hot quarks break free

"Physicists in the US, India and China have calculated that quarks and gluons can break free from their confinement inside protons and neutrons at a temperature of around two trillion degrees Kelvin – the temperature of the universe a fraction of a second after the Big Bang. The researchers arrived at this figure by combining the results of supercomputer calculations and heavy-ion collision experiments. They say that it puts our knowledge of quark matter on a firmer footing."

Quarks break free at two trillion degrees - physicsworld.com

Wrinklons

"A new quasiparticle called the "wrinklon" could help explain why materials as diverse as graphene and household curtains wrinkle in much the same way – despite their very different length scales. The particle has been introduced by researchers in Belgium, France and the US as a result of measurements on a wide range of materials on length scales from micrometres to metres. While the work may not lead to more attractive curtains, wrinkles do turn out to affect the electronic properties of graphene and the analysis could therefore influence the development of graphene-based devices."
Introducing the 'wrinklon' - physicsworld.com

Voyager mission at the edge of the solar system

"Recent data from the spacecraft have shown a gentle decrease in the velocity of the solar wind at the heliopause – the outer boundary of the heliosheath – not the abrupt discontinuity predicted by current theories. Also, scientists looking at other data from both Voyager 1 and Voyager 2 have found that the magnetic field in the heliosheath is a tumultuous foam of magnetic bubbles, as compared to the graceful arcs of magnetic field lines they had expected."
More surprises for the Voyager mission at the edge of the solar system - physicsworld.com

Peer pressure keeps planets young...

"Two US astrophysicists claim they have answered an important question about how planets form: why don't young planets get pushed into their companion stars before they have a chance to grow? It turns out that a little company is enough to keep them there, say the researchers, who argue that multiple planets moving through a rocky disk can prevent one another from falling into the star."

Peer pressure keeps young planets growing - physicsworld.com

Domanda di teoria - entropia

Discutere l'entropia e la forma che essa assume nel caso del gas perfetto

Prima di parlare di entropia dobbiamo ricordare ciò che afferma Clausius

per un generico ciclo reversibile

Allora si ha che il lavoro L dipende dalla trasformazione, Q dipende dalla trasformazione (per esempio, abbiamo visto il calore scambiato a pressione o a volume costante). U ed S non dipendono dalla trasformazione. 

Calcoliamo la variazione di entropia per un gas perfetto:

dQ = dU+dL = dU+pdV

= ncvdT + nRT dV/V

dQ/T = ncv dT/T + nR dV/V

La variazione di Entropia 

Delta S = int_i^f  dQ/T

= ncv int_i^f  dT/T + nR int_i^f dV/V

= ncv ln (Tf/Ti) + nR ln (Vf/Vi) 

Ci possiamo chiedere come si può calcolare la variazione d'entropia nei processi irreversibili. L'entropia (come l'energia interna) dipende solo dallo stato del sistema. 

Posso calcolare la variazione di entropia (anche per i processi irreversibili) considerando una qualsiasi trasformazione reversibile tra gli stessi stati iniziale e finale  della trasformazione irreversibile, 

Consideriamo un'espansione libera di Joule. Un gas perfetto si trova in un contenitore isolato e occupa un volume Vi. Un setto divisore separa il gas da un'altra parte dove c'è il vuoto. Si toglie il setto e il gas espande in modo irreversibile in tutto il volume Vf. 

Per il Primo Principio:  Delta U = Q - L = 0, poiché Q=0 e L=0.

Il gas è perfetto Ti = Tf. Posso immaginare un'isoterma reversibile da i ad f. 

La variazione di Entropia 

Delta S = int_i^f  dQ/T 

= ncv ln (Tf/Ti) + nR ln (Vf/Vi) = nR ln (Vf/Vi) >0. 

Non 'cè variazione di energia interna ma c'è variazione di entropia.

L'entropia ci informa che qualcosa è successo al sistema, il volume è cambiato. 

Calore specifico dei gas perfetti

Il primo principio della termodinamica permette di capire perché, a parità di massa e di aumento di temperatura non è la stessa cosa scaldare un gas a volume costante a pressione costante. Infatti nel primo caso tutto il calore va ad incrementare l’energia interna del gas; nel secondo una parte del calore serve a far compiere al gas un lavoro esterno e perciò ne occorre di più.

Vogliamo mostrare che esiste una relazione tra l’energia interna e i calori specifici dei gas perfetti.

Sappiamo che il calore specifico di una sostanza è definito come:

Nel caso dei gas questa equazione è modificata riferendo il calore specifico non più all’unità di massa della sostanza ma a 1 mole di gas. Quindi:  

Quando un gas scambia calore, la quantità di calore scambiata è diversa a seconda del tipo di trasformazione termodinamica alla quale il gas è sottoposto; in particolare, risultano interessanti i due casi in cui lo scambio di calore avviene rispettivamente a pressione costante e a volume costante. Definiamo:

Per calcolare c_p e c_v per un gas perfetto  dobbiamo scrivere il primo principio della termodinamica che dice che  Q = DU+L, tenendo conto che l’energia interna di un gas monoatomico può essere scritta nel seguente modo: U=Ec=3/2n RT      e quindi:    ΔU = 3/2n RΔT

Uso questa espressione nel primo principio:  Q =3/2nR DT + L

Tenendo presente che quando V=cost si ha L = 0, si ricava: c_v=3/2 R

Tale relazione mostra che il calore specifico a volume costante di un gas perfetto non solo è indipendente dalla temperatura, ma è lo stesso per tutti i gas. Ricordiamo che il valore riportato vale per i gas monoatomici (He, Ne…) per i quali l’energia interna è solo energia cinetica traslazionale. Tenendo conto della cosiddetta relazione di Mayer c_p-c_v = R  si ricava che c_p = 5/2R. Infine otteniamo che:

DU = n c_v DT

Questa è l’espressione generalmente usata per il calcolo della variazione dell’energia interna di un gas perfetto. Allora possiamo scrivere per un gas perfetto il primo principio della termodinamica nella  forma: Q = n c_v DT + L

Se avessimo scelto un gas biatomico invece di uno monoatomico, essendo in questo caso:

avremmo ottenuto per il calore specifico a volume costante il valore c_v = 5/2R  e c_p = 7/2 R. 

Motore di Carnot

Vai al link per vedere l'animazione del funzionamento del motote
http://www.galileo.fr.it/marc/termologia_e_termodinamica/carnot/Carnot_Engine.htm
applet originale © .Wan Ching Hui

Cool microscope feels the heat

"Physicists in Germany have invented a new kind of microscope that uses a gas of extremely cold atoms to map the surface of nanoscale structures. The researchers say that their device is complimentary to atomic-force microscopes (AFMs) and that they ultimately hope to create a probe with precision that is limited only by fundamental quantum uncertainties."

Cool microscope feels the heat - physicsworld.com

Il birraio di Salford

James Prescott Joule FRS (1818 – 1889) was an English physicist and brewer, born in Salford, Lancashire. Joule studied the nature ofheat, and discovered its relationship to mechanical work (see energy). This led to the theory of conservation of energy, which led to the development of the first law of thermodynamics. The SI derived unit of energy, the joule, is named after him. He worked with Lord Kelvin to develop the absolute scale of temperature, made observations onmagnetostriction, and found the relationship between the current through a resistance and the heat dissipated, now called Joule's law.
http://en.wikipedia.org/wiki/James_Prescott_Joule

On the Relation between Heat and the Mechanical Power.

On the Existence of an Equivalent Relation between Heat and the ordinary Forms of Mechanical Power.

By James P. Joule, Esq.

[In the letter to the Editors of the 'Philosophical Magazine.']
series 3, vol. xxvii, p. 205Gentlemen,
The principal part of this letter was brought under the notice of the British association at its last meeting at Cambridge. I have hitherto hesitated to give it further publication, not because I was in any degree doubtful of the conclusions at which I had arrived, but because I intended to make a slight alteration in the apparatus calculated to give still greater precision to the experiments. Being unable, however, just at present to spare time necessary to fulfil this design, and being at the same time most anxious to convince the scientific world of the truth of the positions I have maintained, I hope you will do me the favour of publishing this letter in your excellent Magazine.
The apparatus exhibited before the Association consisted of a brass paddle-wheel working horizontally in a can of water. Motion could be communicated to this paddle by means of weights, pulleys, &c., exactly in the matter described in a previous paper.*
The paddle moved with great resistence in the can of water, so that the weights (each of four pounds) descended at the slow rate of about one foot per second. The height of the pulleys from the ground was twelve yards, and consequently, when the weights had descended through that distance, they had to be wound up again in order to renew the motion of the paddle. After this operation had been repeated sixteen times, the increase of the temperature of the water was ascertained by means of a very sensible and accurate thermometer.
A series of nine experiments was performed in the above manner, and nine experiments were made in order to eliminate the cooling or heating effects of the atmosphere. After reducing the result to the capacity for heat of a pound of water, it appeared that for each degree of heat evolved by the friction of water a mechanical power equal to that which can raise a weight of 890 lb. to the height of one foot had been expended.
The equivalents I have already obtained are; -- 1st, 823 lb., derived from magneto-electrical experiments (Phil. Mag. ser. 3 vol. xxiii. pp. 263, 347); 2nd, 795 lb., deduced from the cold produced by the rarefaction of air (Ibid. May 1845, p. 369); and 3rd, 774 lb. from experiments (hitherto unpublished) on the motion of water through narrow tubes. This last class of experiments being similar to that with the paddle wheel, we may take the mean of 774 and 890, or 832 lb., as the equivalent derived from the friction of water. In such delicate experiments, where one hardly ever collects more than one another than that above exhibited could hardly have been expected. I may therefore conclude that the existence of an equivalent relation between heat and the ordinary froms of mechanical power is proved; and assume 817 lb., the mean of the results of three distinct classes of experiments, as the equivalent, until more accurate experiments shall have been made.
Any of your readers who are so fortunate as to reside amid the romantic scenery of Wales or Scotland could, I doubt not, confirm my experiments by trying the temperature of the water at the top and at the bottom of a cascade. If my views be correct, a fall of 817 feet will course generate one degree of heat, and the temperature of the river Niagra will be raised about one fifth of a degree by its fall of 160 feet.
Admitting the correctness of the equivalent I have named, it is obvious that the vis viva of the particles of a pound water at (say) 51° is equal to the vis viva possessed by a pound of water at 50° plus the vis viva which would be acquired by a weight of 817 lb. after falling through the perpendicular height of one foot.
Assuming that the expansion of elastic fluids on the removal of pressure is owing to the centrifugal force of revolving atmospheres of electricity, we can easily estimate the absoute quantity of heat in matter. For in an elastic fluid the pressure will be proportional to the square of the velocity of the revolving atmosphere, and the vis viva of the atmospheres will also be proportional to the square of their velocity; consequently the pressure of elastic fluids at the temperatures 32° and 33° is 480 : 481; consequently the zero of temperature must be 480° below the freezing-point of water.
We see then what an enormous quantity of vis viva exists in matter. A single pound of water at 60° must possess 480° + 28° = 508° of heat; in other words, it must possess a vis viva equal to that acquired bt a weight of 415036 lb. after falling through the perpendicular height of one foot. The velocity with which the atmosphere of electricity must revolve in order to present this enormous amount of vis viva must of course be prodigious, and equal probably to the velocity of light in the planetary space, or to that of an electric discharge as determined by the experiments of Wheatstone.
* Phil. Mag. ser. 3, vol. xxiii, p. 436. The paddle-wheel used by Rennie in his experiments on the friction of water (Phil. Trans. 1831, plate xi, fig, 1) was somewhat similar to mine. I have employed, however, a greater number of "floats," and also a corresponding number of stationary floats, in order to prevent the rotatory motion of the can.
I remain, Gentlemen,
Yours Respectfully,
James P Joule.

Dal sito


http://www.chemteam.info/Chem-History/Joule-Heat-1845.html

Fermi Telescope and the dark matter

"New results from NASA's Fermi Gamma-Ray Space Telescope appear to confirm a larger-than-expected rate of high-energy positrons reaching the Earth from outer space. This anomaly in the cosmic-ray flux was first observed by the Italian-led PAMELA spacecraft in 2008 and suggests the existence of annihilating dark-matter particles. Physicists believe that about 80% of the mass in the universe is in the form of a mysterious substance known as dark matter. ... researchers are attempting to find direct evidence of it on Earth using either heavily shielded underground detectors or with particle accelerators. But they also have a third, less direct, option – using satellites or balloon-based instruments to detect the particles that some theories predict are created in space when two dark-matter particles collide and annihilate."

Has Fermi glimpsed dark matter? - physicsworld.com

Telescope optics set to aid gravitational detection

"A British team is designing the optics for a telescope that will be able to detect the gravitational effects of violent cosmic events, such as when two black holes collide.
The €790m (£688m) Einstein Telescope should be completed by 2025, by which time it will be capable of detecting gravitational waves around 100 orders of magnitude fainter than current devices can." Telescope optics set to aid gravitational detection News The Engineer

Asta e fune

One end of a uniform beam weighing 30N and 1 m long is attached to a wall with a hinge. The other end is supported by a wire. Find the tension of the rope. What is the action on the wall?

A+T+W=0  (somma vettoriale)

r×W+2r×T=0 (polo in O)

Momento del peso = L m g sin 60°/2

Momento tensione fune = LT sin 30°

  L m g sqrt(3) / 4 = L T /2

   T = 2mg/sqrt(3)

A_x= T cos 60° = mg  ;  A_y= mg-T sin60°=mg-mg/sqrt(3)

n.10 - disco e asta

Un perno P passante per il centro del disco (vedi la figura) permette al disco di ruotare liberamente nel piano della figura che è un piano verticale. Il disco ha raggio b e la sua massa  è m₁ . Una sbarra omogenea e di lunghezza L è saldata al bordo del disco. La sbarra ha la direzione della lunghezza perpendicolare al bordo del disco e si distende solo nel piano del disco. La sua massa è m₂.

Trovare il momento d’inerzia del sistema (disco e sbarra) rispetto all’asse del perno, ossia l’asse perpendicolare al disegno e passante per il centro del disco.

Se il sistema ruota, che direzione ha il momento angolare?

Calcolate l’accelerazione angolare del sistema, quando viene rilasciato dalla posizione mostra in figura.

Calcoliamo il momento d’inerzia ricordando che esso è una quantità additiva. Dato che conosciamo il momento d’inerzia del disco: ½ m₁b², a questo basta aggiungere il momento d’inerzia dell’asta che calcoliamo nel seguente modo. Prendiamo un asse x perpendicolare al perno e diretto lungo l’asta. Supponiamo una piccola massa lunga dx, dm=ρdx, dove ρ è la densità dell’asta pari a m₂/L. Quindi

Discutiamo ora il momento angolare con ω avente la direzione dell’asse del perno, poiché l’asse del perno è quello di rotazione, come ci dice il problema. Facciamo sempre riferimento alla figura usata per calcolare il momento di'inerzia. L'asse di rotazione è l'asse P e usiamo per il calcolo il polo O (il centro del disco) in figura.

Si applica quindi la relazione Iα=τ al sistema.  Il sistema ruota attorno al punto fisso P. Le forze esterne sono l’azione del  sostegno del perno e il peso del disco e dell’asta. Poiché il peso del disco è applicato nel centro del disco , se prendiamo questo centro come polo per il calcolo dei momenti, il peso del disco non ha momento, come l’azione del supporto del perno. L’unica forza che ha momento è il peso dell’asta.

Il momento meccanico è dovuto solo  al peso della sbarra,  m₂g, applicata al CM_sbarra