Magnets MR. BANKS 8 TH GRADE SCIENCE

Transcription

1 Magnets MR. BANKS 8 TH GRADE SCIENCE

2 What is a magnet? A magnet is any material that attracts iron or other ferromagnetic materials. Magnets can be natural or man-made.

3 Ferromagnetic material A Ferromagnetic material is any material that shows strong magnetic properties or are attracted to magnets. silver

4 Ferromagnetic material Iron, nickel, and cobalt are common ferromagnetic materials. Silver

5 Magnetic poles All magnets have two poles. One north and one south. The pole is the part where the magnet is the strongest. Magnetic poles that are unlike attract each other, and magnetic poles that are the same repel each other.

6 Magnetic force Magnetic force is the attraction or repulsion between magnets and ferromagnetic materials. The push or pull made by a magnet.

7 Magnetic force Magnetic force is effected by two factors. The strength of the magnet(s). How far away the magnet is.

8 Magnetic fields The magnetic field is the area of magnetic force surrounding a magnet.

9 Magnetic fields The magnetic field extends out from the magnet and creates an invisible area around the magnet where it exerts magnetic force on objects without touching them.

10 Magnetic fields Magnetic fields can be mapped out using magnetic field lines. The lines start at a north pole and curve through the surroundings and return to a south pole. Arrows on the lines indicate their direction. The lines form complete loops and never cross. The closer together the lines are, the stronger the magnetic field is.

11 Magnetic fields Interactions between magnets have a big effect on the magnetic field of each magnet. When opposite poles are brought together, the field might curve around to the new magnet s pole and not to its own. When the same poles are brought together, the field becomes distorted and flattened.

12 Magnetic fields Where is the magnetic field strongest? Which end of the magnet is the North end? How do you know?

13 Magnetic domains Magnetism is thought to be caused by electrons in an atom spinning a certain way as they orbit the nucleus.

14 Magnetic domains In magnetic materials, these atoms will arrange themselves into microscopic groups. A magnetic domain is a group of atoms with their magnetic fields aligned in the same direction.

15 Magnetic domains In a magnetized material (something that is a magnet) the domains will all point in more or less the same direction. In un-magnetized materials these domains will point in random directions.

16 Making magnets Applying a strong magnetic field to an unmagnetized material causes some of the atoms in the domains to line up with the magnetic field that is being applied to it. This creates a new magnet.

17 Making magnets Two types of magnet can be made. A temporary magnet loses its magnetism quickly (seconds or days) as it s domains revert back to the unmagnetized form. A permanent magnet s domains will remain lined up for a long time (years), thus the material remains a magnet for a long time.

18 Destroying magnets Magnets can be destroyed by knocking the domains out of alignment. Heating the magnet up Hitting the magnet hard

19 Breaking magnets Simply cutting a magnet in half will not destroy it. A magnet will retain its magnetic properties no matter how many pieces it is cut into, each piece will just become another magnet.

20 Earth as a magnet The earth is a giant magnet. The magnetic North/South pole is different from the geographic North/South pole. Currently the magnetic pole is about 1250km (775 mi) from the geographic South pole. Earth s South Pole Earths Magnetic Pole

21 Earth as a magnet The movement of liquid iron around a core of solid iron is thought to be what generates the Earth s magnetic field.

22 Earth as a magnet The magnetic field flips every 0.1 to 50 million years or so. North becomes South and vice versa Currently, the magnetic North pole is in Antarctica.

23 Compass A compass is a device used to detect Earth s magnetic field. Compasses let people easily keep track of which direction is which. This allowed people to travel far distances much more easily and accurately. Compasses are simple devices consisting of a magnetic needle that is allowed to spin freely. The needle lines up with the Earth s magnetic field.

24 Magnetic stripes Evidence of the reversal of Earth s magnetic field can be found on the ocean floor. New ocean floor is added along mid-ocean ridges as the Earth s plates move apart and magma can reach the surface.

25 Magnetic stripes As the rock cools on the surface, the magnetic field of the earth lines up its magnetic domains in the same direction as the Earth s magnetic field. As you go away from the ridge you can observe the direction of the field switch back and forth over and over.

26 Solar wind Our sun is a giant nuclear reaction that releases energy, some of that energy is released as the solar wind. The solar wind, is a constant stream of fast moving, electrically charged particles shout out into space by the sun. This wind is so energetic that is would destroy our atmosphere if it hit us directly.

27 Magnetosphere The Earth s Magnetosphere is formed by our magnetic field and protects us from the solar wind by deflecting the wind around and away from the planet.

28 Auroras A few of the sun s particles will make it through and interact with the particles in our upper atmosphere. The Auroras are lights created when the solar wind hits our atmosphere.

29