1. Magnets
&
How Compasses Work

2. Magnets
Magnetism
Force of attraction or repulsion between two objects.
2 sides to every magnet:
North (N)
Points to magnetic north
South (S)
Points to magnetic south
end

3. Magnets Magnetic Forces Opposites Attract and Likes Repel!!!
Closer to the Pole = Stronger Force
The area that the magnetic force acts on objects is called the Magnetic Field
end

4. Magnets
We draw Field Lines to show the area affected by the Magnetic Field
The arrow goes from North to South
More Lines = Stronger Field
end

5. Magnets
When 2 magnets come close together the Field Lines interact with each other
Remember they go from N to S
Attraction
end

6. Magnets
Repulsion
end

7. So… How does a compass work?
It turns out that you can think of the Earth as having a gigantic bar magnet buried inside.
In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole, as shown in the diagram above.
If you think of the world this way, then you can see that the normal "opposites attract" rule of magnets would cause the north end of the compass needle to point toward the south end of the buried bar magnet.
So the compass points toward the North Pole.
The Compass

8. But what makes the Earth Magnetic?
Our planet’s magnetic field is believed to be generated deep down in the Earth’s core.
Nobody has ever taken the mythical journey to the center of the Earth, but by studying the way shockwaves from earthquakes travel through the planet, physicists have been able to work out its likely structure.
Right at the heart of the Earth is a solid inner core, two thirds of the size of the Moon and composed primarily of iron. At 5,700°C, this iron is as hot as the Sun’s surface, but the crushing pressure caused by gravity prevents it from becoming liquid.
This flow of liquid iron generates electric currents, which in turn produce magnetic fields.

9. How to make a compass SUPPLIES YOU NEED One clear plastic cup
One pencil or pen
One magnet
Thread
One needle or small nail
One cork or piece of foam
The Compass

10. How to make a compass
(1) Rub one end of the magnet along a needle. Always rub in the same direction. Do this about 30 times to magnetize the needle. Test it by picking up a pin.
(2) FLOATING COMPASS. Cut a small piece of cork off and push the magnetized needle through it. Fill the plastic cup with water. Carefully place the cork with magnetized needle into the cup so it is floating in the center.
(3) CHINESE HANGING COMPASS. Tie one end of a short piece of thread to the center of your magnetized needle. Then attach the other end to a pencil and place it over the rim of the plastic cup.
The Compass