Have you ever wanted to defy gravity?
I mean really defy gravity — not the optical illusions we see at “gravity hills” found all over the world.
All you need is a copper or aluminum pipe, preferably 30 centimeters or longer, and a neodymium magnet that is of slightly smaller diameter than the pipe. (Neodymium magnets can be salvaged from old electronics like headphones and hard drives, or you might also have them in a toy set like Buckyballs). Now take the magnet, drop it into the pipe, and watch the gravity defiance begin.
So how does it work? Simple electromagnetism. Electricity and magnetism are related to one another — as electricity flows through a conductor (a material that conducts electricity), it creates a magnetic field. And vice versa, a moving magnet will create electricity in some materials, which also creates a magnetic field.
Aluminum and copper are not magnetic, so when a magnet is dropped in a pipe made of either material, it will not physically stick to it. However, aluminum and copper will conduct electricity if a magnet moves over or under it. So as the magnet falls through the pipe, electricity is produced that creates a tiny magnetic field. This magnetic field, despite its size, is enough to push up against the falling magnet, slowing it down.
This happens because of Faraday’s Law which states that any change in the magnetic environment of a copper tube will cause a voltage to be induced in the copper tubing. This induced voltage causes what are known as eddy currents — electrical currents with circular motions. These eddy currents also produce their own magnetic field, and according to Lenz's Law, when an electromagnetic field is generated by a change in magnetic flux according to Faraday’s Law, the polarity of the induced electromagnetic field is such that it produces a current whose magnetic field opposes the change which produces it.
Essentially, the magnetic field created by eddy current opposes the magnetic field created by the falling magnet. It is this opposition of the two magnetic fields that slows the fall of the magnet.
This is called magnetic braking — since it does not rely on mechanical pressure — and this form of braking is commonly used on most modern roller coasters since traditional friction braking tends to slip or fail if surfaces get covered in water.
Neodymium magnets are very powerful, so be careful not to put your fingers between the magnet and a magnetic surface. Also, I hope I do not have to say this, but keep the magnets away from your mouth. Magnets in the body , especially if there is more than one, can cause dangerous symptoms such as vomiting, diarrhea, and stomach pain, and may require surgery to remove them.
So have some fun, just be safe.
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