17 résultats pour "frictions"

• allumette allumette, petite tige de bois, de carton, ou mèche enduite de cire, dont une extrémité est recouverte d'un mélange de produits pouvant s'enflammer par friction.

• Machine I INTRODUCTION Machine, simple device that affects the force, or effort, needed to do a certain amount of work.

  to decrease the amount of force needed to do work or to change the direction of the force. The wheel and axle and some levers can also be used to increase the speedof performance of a task, but doing so always increases the amount of force needed. A Inclined Plane NutsNuts are pieces of metal with a hole in the middle. They are screwed on the end of a bolt as a fastening. Nuts come invarying shapes, depending on their intended use.© Microsoft Corporation. All Rights Reserved. Ramps and staircas...

• automobile.

  2.1. 3 Allumage Un moteur à explosion à essence est aussi appelé moteur à allumage commandé, car il nécessite la présence d'une étincelle électrique pour enflammer le mélange d'air et de carburant. Cette étincelle est délivrée par une bougie, qu'alimente un courant électrique de haute tension, fourni en général par une batterie et une bobine. En revanche, un moteur Diesel n'a pas besoin de système d'allumage, car l'inflammation du carburant se fait spontanément lors de l'injection du gazole dan...

• Les aéroglisseurs (Sciences & Techniques)

  Les Aéroglisseurs ! L'aéroglisseur A Hovercraft SRN-4 conçu au Royaume-Uni , glisse sur un coussin d'air de 2 ,5 m d 'épaisseur . Propulsé par quatre moteurs de modèle Proteus Rolls Royce , le vaisseau mesure 39 m de long et 28 m de large. Il pèse 160 tonnes pour une vitesse de croisière de 77 nœuds (140 km /h). Les aé ro g li sseu rs o u hovercrafts son t d es vé hi c ules terrestres, marins ou amphibi es, so ulevé s par u...

• Artificial Satellite - astronomy.

  The first stage of a multistage rocket consists of rocket engines that provide a huge amount of force, or thrust. The first stage lifts the entire launch vehicle—with itsload of fuel, the rocket body, and the satellite—off the launch pad and into the first part of the flight. After its engines use all their fuel, the first stage portion of therocket separates from the rest of the launch vehicle and falls to Earth. The second stage then ignites, providing the energy necessary to lift the satellit...

• Technique Kneipp.

  Technique Kneipp Les douches Kneipp Les douches font partie du traitement mis au point par Kneipp. Il s'agi t de diriger sur le corps un jet d'eau à une pression modérée, de telle sorte que l'eau qui s'écoule forme une enveloppe sur la peau. Ce tte technique est sans danger et à la portée de tout le monde. En revanche, les douches sous pression ne doivent être employées que sous surveillance ; elles sont très stimulant...

• Mechanics I INTRODUCTION Mechanics, branch of physics concerning the motions of objects and their response to forces.

  Components of VelocityNeglecting air resistance, a ball thrown into the air at an angle will travel in a parabolic path. The velocity of the ball (V)has independent vertical (V) and horizontal (H) components; the horizontal component stays the same the entire time theball is in the air, while the vertical component, the only component affected by gravity, changes continuously while theball is aloft.© Microsoft Corporation. All Rights Reserved. To understand why and how objects accelerate, force...

• Heat (physics) I INTRODUCTION Heat Loss from a House A thermograph shows the large amount of heat lost through a house's windows during winter.

  Theoretically, the molecules of a substance would exhibit no activity at the temperature termed absolute zero. See Molecule. III TEMPERATURE SCALES Five different temperature scales are in use today: the Celsius scale, known also as the Centigrade scale, the Fahrenheit scale, the Kelvin scale, the Rankine scale, andthe international thermodynamic temperature scale ( see Thermometer). The Celsius scale, with a freezing point of 0° C and a boiling point of 100° C, is widely used throughout the...

• X-Ray Astronomy - astronomy.

  Some neutron stars have weaker magnetic fields that allow incoming material to settle onto the entire surface of the neutron star. Eventually, so much material buildsup that the surface layer becomes dense enough to set off a vast thermonuclear explosion, called an outburst. The explosion heats gas to produce X rays. Such aneutron star—called an X-ray burster—can increase its X-ray production by a million times during an outburst. The X-ray glow fades over time, and the binary systementers a lon...

• From "Resistance to Civil Government" - anthology.

  intending it, as God. A very few—as heroes, patriots, martyrs, reformers in the great sense, and men—serve the state with their consciences also, and so necessarily resist it for the most part; and they are commonly treated as enemies by it. A wise man will only be useful as a man, and will not submit to be “clay,” and “stop a holeto keep the wind away,” but leave that office to his dust at least: “I am too high born to be propertied,To be a second at control,Or useful serving-man and instr...

• Jupiter (planet) - astronomy.

  Beneath the supercritical fluid zone, the pressure reaches 3 million Earth atmospheres. At this depth, the atoms collide so frequently and violently that the hydrogenatoms are ionized—that is, the negatively charged electrons are stripped away from the positively charged protons of the hydrogen nuclei. This ionization results in asea of electrically charged particles that resembles a liquid metal and gives rise to Jupiter’s magnetic field. This liquid metallic hydrogen zone is 30,000 to 40,000 k...

• Guyana 1998-1999 Frictions entre communautés Les tensions entre "Hindous" et "Afro-Guyanais", centrées sur les deux grandes formations politiques, le Parti...

  Guyana 1998-1999 Frictions entre communautés Les tensions entre "Hindous" et "Afro-Guyanais", centrées sur les deux grandes formations politiques, le Parti progressiste du peuple (PPP, au pouvoir) et le Congrès national du peuple (PNC), ne se sont guère atténuées en 1999, malgré la trêve obtenue en juillet 1998 par la Caricom (Communauté des Caraïbes). Le leader du PNC, Desmond Hoyte, qui ne reconnaissait pas la présidente Janet Jagan, a rompu en février 1999 les négociations sur le partage des...

• Steam Engine.

  wear caused by this pressure, steam-engine valves are frequently made in a cylindrical form entirely enclosing the piston, so that the pressure is equal all around thevalve and friction is minimized. The development of this type of valve is attributed to the American inventor and manufacturer George Henry Corliss. In other types ofslide valves, the moving portion of the valve is designed so that steam does not press directly on the back of the valve. The linkage between the piston of the engine...

• Gravitation I INTRODUCTION Gravitation, the force of attraction between all objects that tends to pull them toward one another.

  precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...

• Gravitation - astronomy.

  precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...

• Airplane.

  For example, the Anglo-French Concorde, a commercial supersonic aircraft, was generally limited to over-water routes, or to those over sparsely populated regions ofthe world. This limitation impacted the commercial viability of the Concorde, which ended its regular passenger service in October 2003. Designers today believe theycan help lessen the impact of sonic booms created by supersonic airliners but probably cannot eliminate them. One of the most difficult practical barriers to supersonic fl...

• Belgium - country.

  European Union (EU) directives aimed at improving Belgium’s environmental conditions concern water treatment and water quality, both significant issues in such anindustrial center. Before these directives were issued, the Meuse River, a major source of drinking water, had become polluted from steel production wastes. Otherrivers were polluted with animal wastes and fertilizers. However, Belgium failed to meet EU targets set for the early 2000s for protecting its rivers from farm pollutionand for...