Table of Contents What Is Magnetism? Inside a Magnet Magnetic Earth

- What Is Magnetism? Properties of Magnets A magnet is any material that attracts iron and materials that contain iron A mineral with magnetic properties was first discovered in ancient Greece 2,000 years ago and was named “magnetite” after the city Magnesia. If left to swing freely, a magnet will always point north, where the north star (Polaris) is located.

- What Is Magnetism? Magnetic Poles Magnetic pole – the ends of a magnetic object, where the magnetic force is strongest. A magnet always has a pair of poles, a north pole and a south pole. Magnetic poles that are unlike (opposite) attract each other, and magnetic poles that are alike repel each other.

- What Is Magnetism? Magnetic Force Magnetic Force - the attraction or repulsion between magnetic poles. Can create a push or a pull that can cause an object to move Magnetic forces occur naturally, but can be used by man. Ex. Toy trains

- What Is Magnetism? Magnetic field Magnetic field – the region around a magnet where the magnetic force is exerted. Is strongest at the poles of a magnet, but it surrounds the magnet Can cause magnets to interact without even touching Magnetic field lines – invisible lines that map out the magnetic field around a magnet

- What Is Magnetism? Magnetic Fields Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole.

- What Is Magnetism? Magnetic Fields When the magnetic fields of two or more magnets overlap, the result is a combined field.

A Single Magnetic Field - What Is Magnetism? A Single Magnetic Field Although you cannot see a magnetic field, you can see its effects. The photograph shows iron filings sprinkled on a sheet of plastic that covers one magnet.

Combined Magnetic Fields - What Is Magnetism? Combined Magnetic Fields This picture shows the magnetic field produced when the poles of two bar magnets are brought near each other. Compare the combined field of two like poles to that of two unlike poles.

Magnetic Field Lines Activity - What Is Magnetism? Magnetic Field Lines Activity Click the Active Art button to open a browser window and access Active Art about magnetic field lines.

- Inside a Magnet The Atom The magnetic properties of a material depend on the structure of its atoms. Atom – smallest particle of an element that has the properties of that element. Element – one of about 100 basic materials that make up all matter.

The Atom Atoms consist of: - Inside a Magnet The Atom Atoms consist of: Nucleus - center region of an atom that contains protons and neutrons Proton – a particle that carries a positive charge Neutron – a particle that does not carry a charge.

The Atom Electron – particle that carries a negative charge. - Inside a Magnet The Atom Electron – particle that carries a negative charge. move randomly throughout the atom much smaller than neutrons and protons

- Inside a Magnet Electron Spin A spinning electron produces a magnetic field that makes the electron behave like a tiny magnet in an atom. Electrons form pairs that spin in opposite directions If an atom looses or gains an electron it will increase the atoms magnetic field.

- Inside a Magnet Magnetic Domains Magnetic domain – region in which the magnetic fields of all atoms are lined up in the same direction. If this occurs it creates a magnetic property in an object If the fields are not aligned (pointing in the same direction) then the object does not have a magnetic property.

- Inside a Magnet Magnetic Domains In a magnetized material, all or most of the magnet domains are arranged in the same direction.

- Inside a Magnet Magnetic Materials Ferromagnetic material – a material that shows strong magnetic properties In nature, iron, nickel, cobalt, and gadolinium are common ferromagnetic materials The magnets that we use are usually made from alloys. Alloy – a combination of several metals Ex. alnico – alloy made of aluminum, nickel, iron, and cobalt

- Inside a Magnet Magnetic Materials Modern magnets come in a variety of shapes and are made from many different materials.

Making and Changing Magnets - Inside a Magnet Making and Changing Magnets No magnet can last forever. Magnets can be made, destroyed, or broken apart. Magnets can be made by… placing an unmagnetized ferromagnetic material in a strong magnetic field rubbing the material with one pole of a magnet. Temporary magnet - made from a material that easily loses its magnetism

Making and Changing Magnets - Inside a Magnet Making and Changing Magnets Permanent magnet – made of material that keeps its magnetism. Harder to magnetize Permanent magnets can also be destroyed by… Dropping or striking the magnet Heating the magnet Magnets can also be broken in two.

Making and Changing Magnets - Inside a Magnet Making and Changing Magnets When a magnet is broken, each piece of a magnet retains its magnetic properties after it is cut in half.

Links on Magnetic Materials - Inside a Magnet Links on Magnetic Materials Click the SciLinks button for links on magnetic materials.

- Magnetic Earth Earth as a Magnet Turn to pages 22-23 in your textbooks. Read the first two paragraphs on pages 22 and 23 before beginning section 3 “Magnetic Earth”

- Magnetic Earth Earth as a Magnet Just like a bar magnet, Earth has a magnetic field surrounding it and two magnetic poles.

- Magnetic Earth Earth as a Magnet The magnetic poles are located on Earth’s surface where the magnetic force is strongest. They are located close to the axis poles but not exactly at them (about 1,250 km off) Because of this, a compass will not point directly to the north (axis) pole. Magnetic declination – angle between geographic north and the north to which a compass needle points.

- Magnetic Earth Earth as a Magnet The location of Earth’s magnetic poles does not stay the same. Therefore, the magnetic declination changes over time.

Movement of Earth’s Magnetic Poles - Magnetic Earth Movement of Earth’s Magnetic Poles Earth’s magnetic poles move slowly over time. The data in the table show the position of Earth’s magnetic north pole in specific years.

Movement of Earth’s Magnetic Poles - Magnetic Earth Movement of Earth’s Magnetic Poles Interpreting Data: What is the trend in the speed of the pole’s movement? The average speed of the pole’s movement is increasing.

Movement of Earth’s Magnetic Poles - Magnetic Earth Movement of Earth’s Magnetic Poles Calculating: What is the total distance the pole has traveled over the time shown? Between 1948 and 2001, the pole has moved 857 km (150 km + 120 km +120 km + 180 km + 287 km).

Movement of Earth’s Magnetic Poles - Magnetic Earth Movement of Earth’s Magnetic Poles Predicting: Using the data, predict the average speed of the pole’s movement between 2001 and 2010. Explain.

Movement of Earth’s Magnetic Poles - Magnetic Earth Movement of Earth’s Magnetic Poles The average speed increased by 23 km/yr from 1994 to 2001. That is an increase of 3.3 km/yr per year. There are 9 years between 2001 and 2010. Therefore, a good prediction is that the average speed in 2010 will be 29.7 km/yr.

Earth’s Magnetic Field - Magnetic Earth Earth’s Magnetic Field Since Earth produces a strong magnetic field, Earth itself can make magnets out of ferromagnetic materials. Can attract domains strong enough to line them up in the same direction. Ex. If you left a metal bar lying in a North-South direction for many years, the Earth could magnetize the bar. The same thing may happen to newly formed rocks on the ocean floor.

Earth’s Magnetic Field - Magnetic Earth Earth’s Magnetic Field When molten material hardens into the rock of the ocean floor, the direction of the Earth’s magnetic field at that time is permanently recorded.

The Magnetosphere Earth’s magnetic field affects the movements of electrically charged particles in space and visa versa. Van Allen belts – two doughnut-shaped regions 1,000–25,000 kilometers above Earth that contain electrons and protons traveling at high speed.

The Magnetosphere Solar winds – streams of electrically charged particles flowing at high speeds from the sun Magnetosphere – region of Earth’s magnetic field shaped by the solar wind.

- Magnetic Earth The Magnetosphere The solar wind causes Earth’s magnetic field to stretch out on the side of Earth not facing the sun.

The Magnetosphere Recall from the space chapters…. Aurora – glowing region produced by the interaction of charged particles from the sun and atoms in the atmosphere. In the Northern Hemisphere, an aurora is called the Northern Lights, or aurora borealis. In the Southern Hemisphere, it is called the Southern Lights, or aurora australis.

Click the Video button to watch a movie about auroras. - Magnetic Earth Auroras Click the Video button to watch a movie about auroras.

More on Earth’s Magnetic Field - Magnetic Earth More on Earth’s Magnetic Field Click the PHSchool.com button for an activity about Earth’s magnetic field.

Graphic Organizer Magnets Magnetic fields Magnetic domains produce have atoms grouped in Magnetic fields strongest at mapped by Magnetic domains Magnetic field lines The poles