June 11, 2010
by: Michelle Bertke
Simple iron filings can be used for a variety of interesting experiments and demonstrations. Magnetism is a mysterious concept that can be difficult for students to grasp. Magnetic fields are the forces surrounding a magnet that are identified by how they interact with adjacent magnets and other metal objects. While magnetic fields are ‘invisible’ they can be observed by sprinkling iron filings on a white paper with magnets beneath.
By lightly coating the surface of the paper, the magnetic field will appear as filings align themselves with the field. Different magnets, depending on their strength and shape will create varying patterns in the iron filings. A bar magnet with a distinct north and south will show characteristic lines of a magnetic field. Circular magnets may show multiple lines indicating multiple magnet fields. The stronger neodymium magnets will cause the iron filings to pile up in spikes due to the increased strength. This demonstration can lead to a discussion about magnetic fields: What they are, Where they can be found, and How they are used in the world around us. Read the rest of this entry »
June 1, 2010
by: Martin Sagendorf
We recognize heat & cold, dry & damp, light & dark, and sound & silence. However… I find it absolutely fascinating to consider that we also live within something that we can’t see, hear, touch, or taste.
We all Know:
Our planet has a giant magnet near its core and that its field extends over the whole of the Earth’s surface. But, do we ever really think about this field that passes through soil, rocks, buildings… and us? Granted, relatively speaking this ‘field’ isn’t particularly strong. In fact, it’s a rather weak field when compared to those of a horseshoe magnet or, particularly, a modern Rare Earth magnet.
A Great Demo to show Earth’s Magnetic Field:
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April 2, 2010
by: Ron Perkins
An eddy current is a current set up in a conductor in response to a changing magnetic field. Lenz’s law predicts that the current moves in such a way as to create a magnetic field opposing the change; to do this in a conductor, electrons swirl in a plane perpendicular to the changing magnetic field. Because the magnetic fields of the eddy currents oppose the magnetic field of the falling magnet; there is attraction between the two fields. Energy is converted into heat.
This principle is used in damping the oscillation of the lever arm of many mechanical balances. At the end of the arm a piece of flat aluminum is positioned to move through the magnetic field of a permanent magnet. The faster the arm oscillates, the greater the eddy currents and the greater the attraction to the permanent magnet. However, when the arm comes to rest, the attraction is negligible. Read the rest of this entry »
March 25, 2010
by: Martin Sagendorf
We often think we see forces. However, in reality, we only see the results of forces. To understand forces we must believe in Newton’s Third Law. It states that all forces can only exist in opposite pairs and be equal in magnitude. And… what is very interesting is that Newton’s Third Law does not stipulate that the forces be of the same kind.
Also, by Newton’s Second Law: If the (net) forces are equal, there will be no accelerations (Fnet = ma = 0)… in other words… equal and opposite (net) forces create a state of equilibrium. An interesting example of equal and opposite (and unlike-type) forces is that exhibited by a combination of opposed magnetic fields within a gravitational (force) field. These two different (types) of fields interact purely as ‘force fields’ – only their forces matter… not their types.
The Cosmic Magnetic Puzzle exemplifies a combination of such forces: a barbell containing two ‘donut’ magnets supported in mid-air above stationary pairs of magnets – with an additional pair of donut magnets maintaining the horizontal location of the barbell. Read the rest of this entry »