I mean, I always used to fancy as a kid why can’t we use magnets to keep a fan going in circles? Why can”t we create a perpetual machine using magnets? Even if the magnets get worn out, we can still use them for considerable time. What is the science behind it that makes it impossible?
In: Engineering
How would it work? Once the fan turned a quarter turn or however much it took to align the magnets, it would just stop. Even with a perfectly zero friction axle for the fan (also impossible) you *still* can’t get a fan spinning continuously with magnets unless the magnets are either moving or switching on and off. And of course either of those requires energy input, so by definition that’s not perpetual motion.
Imagine every single magnet as having a spring to every single other magnet.
Either the springs are pulling or pushing.
The key that stops perpetual motion is that no matter how far away two magnets are they are tracking force between them. It doesn’t turn on or off after getting far enough away, the force simply dies down at a predictable constant rate. (Inverse square if I remember correctly)
There’s really nothing for anything to come to. Sure you can twist this web of springs so it sproings back into place but the system is going to eventually fall back into equilibrium. It needs outside power to keep moving
The magnet attracts (or repels) all the fan blades at once so the fan will not spin. You can test this by yourself. Get a fan, make a hole in the tip of each blade. Tie a piece of string to each hole. Pull all the strings at the same time and see what happens. It may rotate a bit but it will immediately get into an equilibrium point and stall
Because an iron piece moving towards a permanent magnet is like a ball moving down a hill.
Eventually, it’ll reach the lowest point it can reach and stop moving.
After that, you’ll need to move the ball up the hill before it can move again, and moving it back to its starting position takes as much energy as you could get out of it moving down the hill in the first place.
Magnets are not a source of energy; they are just a way of transferring energy from one place to another.
Not to mention you can’t exactly “point” where magnetism starts and ends.
Energy can neither be created nor destroyed.
Friction from rubbing generates heat. Heat is a form of energy, therefore this increase in heat must mean a decrease in energy somewhere else. The source would be motion, so anytime you have friction you have loss of motion.
If you could create a frictionless fan, something that never touched anything maybe you could have a perpetual motion machine?
Note that if you tried to use this fan to power anything you’d be pulling energy out of its motion and it’d slow down.
Adding magnets is similar to digging in the ground and making hills and valleys.
When you’re done, and you put a marble/iron ball on the top of a hill, it will roll around for a while.
But no matter how you set things up, eventually friction will slow the ball down and stop it.
As a child I once had an idea to put magnets facing all North polarity inwards on a sphere, using ridiculous amounts of superglue to hold them to the surface of the ball bearing. There were tiny gaps, where there would be an intense North polarity magnetic field, but for the most part this made a “bubble” you could feel on the sphere where it was primarily South magnetic field, about 2 inches above the surface of the magnets. The North areas were really weak polarity, the South areas were strong enough to hold the weight of the magnets glued together.
I then made a bowl lined with magnets, South polarity upwards. You see where this is going, right? I can balance the sphere above the bowl and spin it, and it should spin until air resistance stops it. I planned to remove air resistance from it, by putting it in a vacuum chamber with no air. If I could spin it fast enough to still be moving once the air was gone, it would never stop!
If that worked, the next step was obvious – I would wrap it in copper coils and generate an endless stream of electrical power. I had discovered the secret to perpetual motion, and was going to use it to generate electricity. Maybe not much at a time, but with enough of these and built better than my 10 year old hands could do with store bought magnets and superglue I could possibly make this work.
Then I happened to be on Wikipedia falling down a black hole of information, clicking link after link whenever I saw a new term to learn about, you know, the thing normal people do with Tumblr…
Anyways, long story short Lorentz Force is what you’re looking for. When you move the magnet near enough to a wire to generate electricity you’ll also generate *heat*. That lost energy produces a backwash effect – the energy in the copper is going slower than the magnet is spinning because it lost energy, and electricity in a wire generates a magnetic field. The magnetic field allows the wire to affect the spinning magnet, and since the electricity in the wire is slower it drags the magnet to a stop eventually.
So now I had a brand new problem – I could, in theory, make a perfect magnet and perfect base, put them in a perfect vacuum and make it spin forever. Here is where I’m permanently stuck – no matter where I go from here, *I can never extract more energy from the magnet than I initially put into it*. It will always slow down at the same rate or faster than the work being done by the electricity it generates.
It’s a bit long winded, and perhaps not quite ELI5, but I hope this helps add a layer of fun information to what others are saying here.
It’s just not possible.
Essentially:
The electricity produced by the system is being sent, or used by something. That means that energy is losing the system.
Without energy being constantly reintroduced into the system, it will run out.
It may not be fast, but it will eventually run out. Either by a magnet or battery slowly losing charge, or heat destroying the materials, or momentum being lost. Eventually, whatever is “creating” the enegy will lose out to friction, or time, or loss of mass.
There are, however, long lasting means of producing energy that are near-endless, like solar power, the waves up and down oscillation motion in the seas, ocean currents, etc. that can be harnessed, but it’s not a perpetual closed system in the way a perpetual motion machine is envisioned.
Even if you found a way to use the rotation of the earth to spin a gear, eventually the earth would stop spinning from loss of kinetic energy, however long it took (billions or trillions of years)
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