Magnetism

The Nature of Magnets ► ► Magnetism: force of attraction or repulsion   Attraction to any substance that is, or can become, a magnet ► ► Rule of magnets:   Opposite poles attract   Like poles repel ► ► Magnetic fields: area surrounding the magnet that influences other objects ► ► Poles: region of magnet where effects of magnet are strongest

A single magnet

Two magnets

► Magnetic domains: groups of atoms lined up together  unmagnetized: groups are in random patterns  magnetized: atoms all (or mostly) line up in one direction ► Magnets made of iron, cobalt, nickel  Called ferromagnetic (“ferro-” for Fe or iron-like)  Atoms can rearrange to line up in these materials What causes magnetism?

Domains

The Earth as a magnet ► Demonstration of magnet and “lodestone” ► compass always points to North ► Why? ► The earth itself is a magnet  strongest force is at the poles of the magnet (The North and South Pole!)  Inner core of molten iron and nickel spinning

► Poles switch about every 500,000 years  evidence in rock samples

The Sun’s Effect on Earth ► ► Solar wind: charged particles from the sun would destroy us if earth had no magnetic field ► ► Cause interference for TV, Cell phones ► ► Auroras: Northern and Southern Lights   charged particles hit atmosphere at the Poles and cause the air to glowtmosphere at the Poles and cause  Video of Auroras Video of Auroras Video of Auroras in Finland Auroras in Finland

► Brainpop on magnetism Brainpop on magnetism Brainpop on magnetism ► DVD on magnetism