|MadSci Network: Physics|
Hi Curtis, Good question. Aluminum normally is not magnetic. Aluminum is an electrical conductor. When the aluminum disk is placed near the magnet, the magnetic field exerts a force on the electrons in the aluminum. The magnetic force will cause the electrons to separate from the positively charged atomic nuclei. A portion of the disk will then become charged. Because the disk is spinning, the charges will move around the circumference of the disk. The movement of electrical charge is an electrical current. The electric current generated will have a magnetic field that is equal and opposite to the field of the magnet. The induced magnetic field is what exerts the force on the magnet. A good method to determine the induced force is by measuring the energy required to spin the disk. More energy is needed to spin the aluminum disk to the same speed when the magnetic field is present. A stronger magnetic field, or faster rotation of the aluminum disk, will require more energy to maintain the same rotational speed. Bob Novak Specialist - Process R&D Carpenter Technology
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