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### Course: Physics library>Unit 18

Lesson 1: Discovery of magnetism

# Compass: Which way is north?

A compass is a device that shows direction by using a magnetized needle that always points towards the earth's northern magnetic pole. This video shows how to make a compass using a magnetized needle and a styrofoam ball floating on a dish of water. Created by Brit Cruise.

## Want to join the conversation?

• 1) Can ceramics be magnetized?
2) Why does a magnetized substance or a magnet only point towards north, and not any other direction, or even up or down?
3) How do naturally occurring magnets form (or occur) ?
4) Do all planets have a magnetic field like Earth? If so, how do they occur?
5) Why are not all rocks and minerals magnetized?
6) Is there any particular place on Earth where naturally occurring magnets are to be found in the highest concentration?
There is no need for a single person to answer all the questions! Thanks!
• 5) iirc, the main magnetic materials are iron, nickel and cobalt, although at least some lanthanides can also be magnetic when in alloys - e.g. neodymium-iron-boron can make a very powerful "rare earth" magnet.
Many rocks contain quite a bit of stuff such as calcium (e.g chalk) or silicon (e.g sand/sandstone etc. etc.). which are not magnetic.
• So the camera is facing southeast right?
• And one more thing bye the way the man made compass in this video did point correctly in the north direction like any real compass could have . thanks to the water in the plate & the needle pierced through the plastic material that enabled the needle to float & then slowly align itself with earth's magnetic field & end up pointing in the north direction .
(1 vote)
• So how can you tell which way is north? I've heard of something like this before.
• It depends on which charged side you rub the needle with. If he rubbed it with north side, then the needle was magnetized in a way that its pin points at the north magnetic pole, which is the south geographic pole.

If you were to take a map of the world you'd have to look down to see the geographic south pole.
• In the first half of the video he's rubbing the rock on the needle or pin. What is he doing?
• He is rubbing the rock on the needle. The rock may contain iron so it's like a magnet. Rubbing a magnet on a metal or steel that's not a magnet will make that object a "temporary magnet." So really what he is doing is making the needle into a "temporary magnet."
• i have heard that the magnetic pole is shifting is it true if yes why?
• Yes, Geomagnetic shifts do occur. However the factors as to why are rather complex, and involve underlying factors in the earths structure
• is it possible to destroy Earth's magnetic field
• Yes its possible and the above theory is correct.
Anyways you wont be alive to see this, so it's of no use.
• how would we get to know that which side is north ?
• 1) there is a circular argument that you can work out which end of the magnet is north if you know which way the needle points, and you can work out which way the needle points if you know which end of the magnet is north!
If you know neither, then it doesn't help.

2) You can work out which way the needle points by looking at the Sun (in the daytime),
If you are in the Northern Hemisphere (excluding the tropics), which is most of us (!), then the Sun rises in the east (left) moves across the south, and sets in the west (right).
- so just wait until lunchtime and see which way the needle points! (remember, the Sun is in the South at that time!)

3) If in the Southern Hemisphere (excluding the tropics) - e.g. Australia and some parts of South America, the sun goes east-north-west, so, again, you can see which way the needle points.

4) Having worked out the needle, you can then work out which way round the poles on the magnet are,
Having worked out one magnet, you can work out any other.

5) It is also why compasses appear to have been first used for navigation by countries outside the tropics - indeed, China, which is often credited with the invention of the navigational compass, lies mostly north of the tropics, so the Sun can be used as a device to orientate the magnetised needle.

6) If you prefer the invention of the navigational compass to have been the Vikings, or in the Middle East (much of Saudia Arabia and Egypt, as well as "Babylon" and "Persia" are also north of the Tropics), or even in Mexico (half of which is north of the Tropics), then, from a practical point of view of the sun-orientation method, all are theoretically possible.

7) So, to summarise, if you are outside the tropics, you magnetise the needle EITHER WAY, then use the Sun to work out which end of the magnetised needle is which.
Hope this helps.
• how would you know which way is north if you had no reference? Can the direction of stroke alone tell you this? Are you sure?
• I would conjecture that the effect of rubbing one end of a "bar" magnet on the needle would polarise the atoms of the needle in one direction, while using the other end of the magnet would polarise the atoms the other way - i.e. north and south reversed.
So I would conjecture that "North" cannot be found without an external reference.
The position of the Sun would be a suitable external reference, because it always rises in the East, wherever you are on the surface of the Earth.
Like all basic science problems, the best way is to try it at home and see!
I'm sure you will be able to find a needle and a "bar" magnet to check it at home!