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Chapter 21 Magnetism Section 1 - What is Magnetism? Pages 550 - 554 Early Uses of Magnetism • Thousands of years ago, people noticed that a mineral called magnetite attracted other pieces of magnetite and bits of iron. • When pieces of iron were free to turn, one end pointed north north. • These might have been the first compasses compasses. • The compass was an important development for navigation and exploration exploration. • Ancient writing suggests that 2,000 years ago, Egyptians used magnets to make statues float! Magnets • Magnets attract objects containing iron, nickel, or cobalt, such as nails and paper clips. • Magnets can also attract or repel other magnets. • Every magnet has two ends or poles poles….a north pole and a south pole. • Like poles repel each other and opposite poles attract each other. The Magnetic Field • Remember a force is a push or pull that causes an object to move move. • A magnetic force can be exerted even when objects are not touching (just like gravity gravity). • The magnetic force becomes weaker as the magnets get farther apart. apart • The magnetic force is exerted through a magnetic field. field Field Lines • Magnetic field lines begin at a magnet’s north pole and end on the south pole. • The field lines are close together where the field is strong and get farther apart as the field gets weaker weaker. • According to the diagram, where is the magnetic field the strongest?. poles. • Near the poles Attraction and Repulsion • Field lines that curve toward each other show attraction. attraction • Field lines that curve away from each other show repulsion repulsion. Making Magnetic Fields • A moving electric charge, such as a moving electron, creates a magnetic field. electron • A group of atoms, with their fields pointing in the same direction, is called a magnetic domain. domain Magnetic Domains • Microscopic sections of iron and steel act as tiny magnets. • Normally, these domains are oriented randomly and their magnetic fields cancel each other. • When a strong magnet is brought near the material, the domains line up, up and their magnetic fields add together. Earth’s Magnetic Field • Earth has a magnetic field similar to the field of a bar magnet. • The region of space affected by Earth’s magnetic field is called the magnetosphere magnetosphere. • One theory is the shifting of molten iron in the outer core of the Earth caused Earth’s magnetic field. Nature’s Magnets • Some animals use natural magnets to detect Earth’s magnetic field to help them navigate. • Instead of using compasses, honeybees, rainbow trout, and homing pigeons have little pieces of magnetite in their bodies. Earth’s Changing Magnetic Field • Earth’s magnetic poles do not stay in one place. place • The magnetic pole in the north is in a different location than where it was 20 years ago. ago • Sometimes Earth’s entire magnetic field reverses direction! (North Pole become South) direction • This has happened more that 70 times in the past 20 million years. The Compass • A compass needle is a small bar magnet with a north and south magnetic pole. • The north pole of the compass needle points toward Earth’s north magnetic pole. pole