Magnetism ESCI 215 Chapter 6

Magnetite Magnetism was discovered more than 3000 years ago Certain rocks (magnetite) attracted bits of iron Magnetite formed from the slow hardening of the earth’s crust The earth’s magnetic field made it magnetic Magnetite was used by sailors in 1200 BC to point the way north This allowed them to always know which way they were going regardless of weather, day/night, etc.

What Causes Magnetism? Substances are made up of atoms Atoms can have a positive or negative charge In non-magnetic substances (i.e. paper, wood, plastic), the atoms group together in opposite charges (positive-negative) and cancel each other out In magnetic substances, atoms group themselves into small regions – magnetic domains – an arrange themselves randomly When a magnet is brought near, the domains line up and the substance is attracted to the magnet On magnets, the positive end is called North and the negative end is called South On the Earth, the North pole has a negative charge and the south pole has a positive charge

What do Magnets Attract? Non-metallic objects are not attracted Not all metallic objects are attracted Only iron, nickel, cobalt are attracted Some combinations of metals are attracted Iron, aluminum, nickel, cobalt mixed together Aluminum on its own is not magnetic (Events 6-A and 6-B)

Magnetism is a Force Magnetism is a force Magnets have a magnetic field and it is a force that attracts magnetic substances Event 6-C shows how iron filings will line up along this force Unlike poles are attracted (N and S) and like poles are repelled This magnetic field acts through certain materials (i.e. paper, glass, copper, wood, aluminum foil) and is blocked by others (i.e. iron, steel) Any material that is magnetic will block the line of force Event 6-D

Temporary and Permanent Magnets Temporary magnets (Electromagnets) The magnetic force can be turned on and off using an electric current Permanent magnets Stay magnetic for long periods of time if handled carefully Lose magnetism by: Placing it in a powerful external magnetic field Heating it too much Hitting or dropping it

How to Make a Permanent Magnet Materials: Hard steel (i.e. hacksaw blade, sewing needle, darning needle, workshop file) Magnet Methods: Hold the hard steel and stroke it 20 – 30 times with a magnet

How to Make a Compass Materials: Methods: Magnetized needle Cork Plastic or glass container Water or oil Methods: Fill the container with the liquid, put the slice of cork in the liquid and put the needle on the cork Observe the direction the needle moves to (N)

Assessment and Instruction Students could make a compass and write a summary how it works and how they know which end points north What can the students say about the poles of the needle? Do they use vocabulary such as magnetic poles, domains, magnetic field? Check website listed on page 101

Discussion Where does this topic fit into the Science curriculum? Which grades and strands? Which curriculum objectives relate to the discrepant events?