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Multiplying forces

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  Terms, units, and abbreviations These metric units are used: force, effort or load in newtons (N) work in joules (j) power in watts (W) The equivalent customary units and conversion factors are as follows: 1 newton — 7.23 poundals 1 joule = 23.73 foot poundals 1,000 watts or 1 kW = 1.34 horsepower A machine is defined in physics as a device for applying or transmitting mechanical power. Its function may be to overcome resistance to motion or to change of shape or size at one point of an object by applying a force, often at some other point The multiplication of forces is possible in mechanical devices, enabling work to be performed that human strength alone could not do. Two terms commonly used in describing machines are work and power; both of which have been given precise, technical meanings. In a simple machine, the work done is equal to the product of the load (a force) and the distance it moves in the direction of the force, irrespective of the time taken; it
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Equilibrium of physics

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 Statics is concerned with bodies that are in equilibrium , which is the state of an object when it is not accelerated; a body that is at rest or moving at constant velocity is therefore in equilibrium . For an object to be in equilibrium it is necessary for all the forces acting on it to cancel each other out exactly. Center of gravity The concept of center of gravity is used in determining the stability of an object’s equilibrium : The center of gravity is the point where the entire weight of an object can be considered to be concentrated. A disk, for example, has its center of gravity at the center, whereas that of a rigid triangular sheet lies at the point of intersection of the lines that join the vertices of the triangle to the midpoints of the opposite sides. The center of gravity of an irregularly-shaped flat object can be found by suspending it from any two points on it and marking the point of intersection of a plumb line suspended from each point in turn.
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Statics of physics

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  Terms, units, and abbreviations The following units are used: length in meters (m) mass in kilograms (kg) weight in newtons (N) density in kilograms per cubic meter (kg m-3) The equivalent customary units and conversion factors are as follows: 1 meter = 1.09 yards or 3.28 feet • kilogram = 2.20 pounds 1 newton = 7.23 poundals 1,000 kilograms per cubic meter = 62.43 pounds per cubic foot Time is measured in seconds (s) in both systems of units. Statics is the branch of physics that deals with the analysis of bodies that are held stationary under the influence of a system of forces. Using statics it is possible to predict what will occur when the forces acting on an object are changed, the size of the forces needed to keep an object stationary, and many other phenomena of interest to physicists and engineers. Forces The study of statics depends crucially on an understanding of the concept of force, which can be defined as an agent that is capable
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Breaking the cold barrier: superconductivity

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  A train floats along, frictionless, on a magnetic cushion above the tracks. Electrical wires deliver power to homes and industries over long distances without any loss of energy. Supercomputers perform calculations with 50 times the speed of the fastest computers available today. These are a few of the advances scientists believe are coming closer to reality as advances in high-temperature superconductivity continue. Magnetic resonance imaging (MRI) , shown above, produces images of tissues inside the body. Doctors use these images to diagnose diseases and injuries. Reamde more Breaking the cold barrier: superconductivity
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Unusual states of matter

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 Some substances exist in states that do not comply with the normal definitions of a gas, a liquid, or a solid. For example, jelly is neither a true solid nor a liquid, and smoke is neither a pure gas nor a solid. Matter in stars and in the tails of comets exists as a plasma, a mixture of charged particles that is outside the normal definition of a gas. In general, a plasma can exist only at extremely high temperatures. At extremely low temperatures, approaching absolute zero, some materials take on remarkable properties. Although they are strictly not different states of matter, their exceptional behavior is also described in this article. Mist is an unusual state of matter, despite being a familiar phenomenon. It is a colloid in which the dispersion medium is a gas (air) and the disperse phase is a liquid (water droplets). In physical terms, fog and cloud are similar types of colloids. Reamde more Unusual states of matter
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Alloys, solutions, and mixtures

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 When two substances are mixed together, they may react to form a chemical compound, if they do not react, they form a mixture. The constituents of a chemical compound cannot be separated by physical or mechanical methods. The constituents of a mixture, on the other hand, can be separated. For example, a mixture of salt and sand can be separated by dissolving the salt in water. And a solution of salt in water can be separated by evaporating or distilling off the water. Alloys are made by melting together a metal and one or more other substances (usually also metals) to produce a new material with different physical properties. Alloying aluminum with copper, for example, produces an alloy with a greater hardness, although with less than 60 per cent copper the melting point is lowered. All alloys of zinc and copper, on the other hand, have melting points higher than that of pure zinc. Alloys An alloy consists of a metallic element and one or more other, usually metallic,
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Properties of gases

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In a gas , the atoms or molecules are free to move about rapidly. Collisions with the walls of the container give rise to gas pressure. Because the atoms or molecules of a gas are far apart and move independently of each other, a gas can be expanded or compressed to a much greater degree than can a solid or a liquid. Changes in volume are accompanied by changes in pressure and/or temperature. These changes can be explained in terms of the kinetic theory of gases and the gas laws.
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