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Magnes, while tending his flock, noticed that pieces of a certain type of rock were attracted to the nails on his shoes and to his metal staff. This phenomenon was called magnetism and, as time passed, further studies of the behaviour of this rock revealed several curious effects. For example, a piece of this rock could either attract or repel another similar piece. This effect seemed to result from two different magnetic effects, so investigators thought that there must be two different types of "magnetic ends," or poles, on the rock. This observation led to the law of magnetism, which states:Like magnetic poles repel and unlike poles attract each other.In 1269, Pierre de Maricourt was mapping the position of a magnetized needle placed at various positions on the surface of a spherical piece of this rock. He observed that the directions of the needle formed a pattern that encircled the rock, like meridian lines, and converged at two points on opposite ends of the rock. When this rock was then suspended by a string, the two converging points tended to align along Earth's north-south axis. This property of the rock earned it the name "lodestone" or "leading stone." Maricourt called the end pointing northward the north-seeking or north pole and the end pointing southward the south-seeking or south pole. All magnets have both poles. Lodestone, which contains the mineral magnetite (Fe3O4), was later used in the development of compass technologyMagnetism plays a major role in your everyday life. All electric motors, with uses as diverse as powering refrigerators, starting cars, and moving elevators, contain magnets. Magnetic resonance imaging (MRI) has become an important diagnostic tool in the field of medicine, and the use of magnetism to explore brain activity is a subject of contemporary research and development. Other applications of magnetism include computer memory, levitation of high-speed trains, the aurora borealis, and, of course, the first important historical use of magnetism: navigation. You will find all of these applications of magnetism linked by a small number of underlying principles. In this course , you will learn that both the internal properties of an object and the movement of charged particles can generate a magnetic field, and you will learn why all magnetic fields have a north and south pole. You will also learn how magnetic fields exert forces on objects, resulting in the magnetic alignment that makes a compass work. You will learn how we use this principle to weigh the smallest of subatomic particles with precision and contain superheated plasma to facilitate nuclear fusion.

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