It is often said that the magnetic energy, stored in a permanent magnet, cannot be practically harvested; converted (transduced) to kinetic energy (the energy an object possesses due to it’s motion), or any other form of useful energy, because it takes more external energy (from an outside source) to do (effect) that conversion. Stated differently; it is not possible to get any net amount of work out from a permanent magnet, over and above the work that it takes to get that amount of work out, because it takes more outside work, than the work that can be, ultimately, produced by that permanent magnet, from utilization of that outside work.
A simple (pretty) experiment will suffice to prove this assertion wrong.
Take five steel balls (spheres), a neodymium cylinder permanent magnet, some plastic molding (track for the steel balls to roll on), and some wood to make ramps for that molding. (See, Brady Haran’s You-Tube Video of this experiment made for the University of Nottingham titled; “Momentum, Magnets, and Metal Balls - Sixty Symbols”).
Set up the track so that there is a slight incline at the beginning that levels off, relatively soon.
Connect four steel balls, magnetically and linearly, to one end of that cylinder magnet and place that arrangement in the middle of the track, at the bottom so that the bare end (with no steel balls attached) of that cylinder magnet faces the direction from where the fifth steel ball will come.
Cause (lift up, place, and slightly nudge) the remaining fifth steel ball to roll down from the top of the track, from that slight incline, towards the bare end of that cylinder magnet. Notice that this steel ball will roll down that slight incline, picking up speed, and reaches a constant, but relative slow, speed, as it levels off.
As that slow, but constantly, moving steel ball enters the magnetic field of that cylinder magnet, it speeds up, dramatically. The magnetic energy (pull force) of that cylinder magnet causes it to speed up so.
Notice that, when that steel ball hits that cylinder magnet, the fourth steel ball, away from the other side of that cylinder magnet (loosely held by that cylinder magnet) ejects, at high speed, traveling for some distance away before it comes to rest.
In physics, a force does work if, when acting on a body (usually, an object) there is a displacement (usually, distance traveled) of the point of application in the direction of the force.
In this experiment, the external kinetic energy applied came from both, the lifting of the fifth steel ball (a short distance at slow speed), to overcome gravity and, the nudging of it (also a short distance at slow speed) to get it rolling down the slight incline. From this little bit of work, the fourth ball, (magnetically held, loosely, by the cylinder magnet), was caused to eject (a long distance at high speed). In other words, for the little bit of work we put into this system, we got a lot more work out from it.
Since, according to the Law of Conservation of Energy, energy of an isolated system remains constant, is conserved, (it is neither created nor destroyed but does change form), the extreme amount of additional energy which caused that extreme amount of additional net work in this system, over and above the relatively small amounts of external kinetic energy required to effect it, had to come from that cylinder magnet.
This experiment proves that it is not only possible to harvest the magnetic energy stored in a permanent magnet to perform useful work but, that it won’t cost more (in external energy or external work) to do it.
Dan
PS:
A simple (pretty) experiment will suffice to prove this assertion wrong.
Take five steel balls (spheres), a neodymium cylinder permanent magnet, some plastic molding (track for the steel balls to roll on), and some wood to make ramps for that molding. (See, Brady Haran’s You-Tube Video of this experiment made for the University of Nottingham titled; “Momentum, Magnets, and Metal Balls - Sixty Symbols”).
Set up the track so that there is a slight incline at the beginning that levels off, relatively soon.
Connect four steel balls, magnetically and linearly, to one end of that cylinder magnet and place that arrangement in the middle of the track, at the bottom so that the bare end (with no steel balls attached) of that cylinder magnet faces the direction from where the fifth steel ball will come.
Cause (lift up, place, and slightly nudge) the remaining fifth steel ball to roll down from the top of the track, from that slight incline, towards the bare end of that cylinder magnet. Notice that this steel ball will roll down that slight incline, picking up speed, and reaches a constant, but relative slow, speed, as it levels off.
As that slow, but constantly, moving steel ball enters the magnetic field of that cylinder magnet, it speeds up, dramatically. The magnetic energy (pull force) of that cylinder magnet causes it to speed up so.
Notice that, when that steel ball hits that cylinder magnet, the fourth steel ball, away from the other side of that cylinder magnet (loosely held by that cylinder magnet) ejects, at high speed, traveling for some distance away before it comes to rest.
In physics, a force does work if, when acting on a body (usually, an object) there is a displacement (usually, distance traveled) of the point of application in the direction of the force.
In this experiment, the external kinetic energy applied came from both, the lifting of the fifth steel ball (a short distance at slow speed), to overcome gravity and, the nudging of it (also a short distance at slow speed) to get it rolling down the slight incline. From this little bit of work, the fourth ball, (magnetically held, loosely, by the cylinder magnet), was caused to eject (a long distance at high speed). In other words, for the little bit of work we put into this system, we got a lot more work out from it.
Since, according to the Law of Conservation of Energy, energy of an isolated system remains constant, is conserved, (it is neither created nor destroyed but does change form), the extreme amount of additional energy which caused that extreme amount of additional net work in this system, over and above the relatively small amounts of external kinetic energy required to effect it, had to come from that cylinder magnet.
This experiment proves that it is not only possible to harvest the magnetic energy stored in a permanent magnet to perform useful work but, that it won’t cost more (in external energy or external work) to do it.
Dan
PS:
James Clerk Maxwell (June 13, 1831 - November 5, 1879)
