Magnetism (magnetic forces)

1. The attraction or repulsion between magnetic poles Magnetism (magnetic forces)

2. Properties of a magnet • Magnets attract iron and materials that contain iron • Magnets attract or repel other magnets • One part of a magnet will always point north when allowed to swing freely (no matter the shape of the magnet)

3. Magnetic Poles & Magnetic Force • Every magnet has a North magnetic pole and a south magnetic pole • Poles that are “like” (N&N or S&S) repel one another • Poles that are “unlike” (N&S) attract one another • This attraction or repulsion between magnetic materials is called magnetic force

4. Magnetic Field Magnetic force is strongest at the magnetic poles of the magnet • The area of magnetic force around a magnet is its magnetic field • Mapped using magnetic field lines • Single Magnetic field is the m. force around one magnet • Combined magnetic field is the forces around two magnets

5. Magnetic Fields Cont’ • Combined magnetic field is the forces around two magnets • The combined magnetic field of “like” poles looks different from the combined magnetic field of “unlike” poles • Combined magnetic field is always stronger then single magnetic field

6. Magnets • What gives magnets their magnetism? • Each electron has a spin causing a magnetic force to develop • Since electrons normally travel in pairs, they spin opposite directions, cancelling out the magnetic force

7. Magnetic materials • If a material is magnetized, its magnetic domains are aligned • Materials that show strong magnetic properties are called ferromagneticmaterials (nickel, iron, cobalt, etc.) • Permanent magnets keep their magnetism for long periods of time • Temporary magnets only keep their magnetism for a short period of time

8. Breaking and Destroying Magnets • If you break a magnet what happens? • You just get two new magnets. • How do you destroy magnets? • Heat them • Drop them • Strike them hard

9. Earth’s Magnetism • Earth is like a bar magnet: • It has a magnetic field • It has two magnetic poles • Earth’s Iron core is what helps cause the magnetism • It’s what causes a compass to work • Earth can make magnets out of ferromagnetic material because its magnetic field is so strong

10. Magnetic Declination • Earth has a geographic north pole and a magnetic north pole • Magnetic declination is the angle of difference between the two • Naturalists use magnetic declination maps like this for direction

11. Earth’s Magnetism • Molten material under Earth’s crust pushes through cracks deep in the ocean, causing the sea floor to spread • As the molten material cools and hardens, its iron aligns with Earth’s magnetic field. • Scientists have found that the hardened rock on the ocean floor has alternating magnetic domains, sot hey can infer that Earth’s magnetic field has reverse many times in the past.

12. Magnetosphere, Solar wind, Auroras • Earth’s magnetic field affects the movements of electrically charged particles in outer-space. • Solar wind is a stream of those particles flowing at high speeds from the sun • Magnetosphere is the earth’s magnetic field shaped by solar wind • Van Allen Belts are the rings above earth’s surface that contain protons and electrons travelling at very high speeds • Auroras are the glowing regions in Earth’s atmosphere caused by solar wind

13. Auroras