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
a magnet has a north and a south pole. it might push away in one direction yes, but it attracts in a different direction so the overall motion cancels out.
moving a fan also creates friction, which induces heat, which is a form of energy. you cant generate infinite energy out of nowhere because energy is conserved in our universe (as far as observed).
Because not even does a magnet pull on metal, but thr metal also pulls on the magnet. It would be like trying to move a car by pressing against it from the inside.
Also, if you think something like rotating things, there will always be some form resistance that will gradually slow things down.
Because it is not possible to arrange permanent magnets in a way that would create a continous spinning. Even if you arrange the magnets in a circular way, then it will just move for a moment, until it stops.
For continous rotations you require changing magnets. So basically you need to switch magnets on or off or move them around. However that requires energy from the outside and thats basically how electric motors work.
Magnets for all we care during our lifetimes are “perpetual”. The problem is that you eventually need moving parts that cannot levitate and will eventually wear out due to friction
If a magnet’s north pole pushes away, then imagine rolling a ball towards a hill. It will slow down and eventually turn around and roll back down. It will take energy to get the ball to the top of the hill.
If a magnet’s south pole pulls, then imagine rolling a ball into a valley. It’ll roll faster and faster until it reaches the bottom and stop there. Taking it back out of that valley will need energy.
There’s no configuration of hills and valleys that will make a ball roll forever up and down. Likewise, there’s no configuration of north and south poles that will allow for something to move forever.
I’m going to go back further than magnets.
We can’t use ***anything*** for perpetual motion, as it breaks the laws of thermodynamics.
And ***nothing*** can break the laws of thermodynamics.
You can use gravity to move stuff. If you like, you can push a cart full of bricks up to the top of a hill. Then you can attach a rope to the cart, and let the cart roll back down, and it’ll pull on the rope. You can use that to do work.
But what you *can’t* ever do, is get more work out of the cart rolling down the hill, than you spent on pushing it up the hill. Every downhill movement of the cart, must be paid for, sooner or later, with an equal uphill movement. There’s no shortcut you can take from the bottom of the hill to the top, without spending energy to get there.
The same thing is true with magnets. You can push the repelling poles of two magnets together if you like, and then if you release them, the repulsive force will make them move away from each other. But just like the cart on the hill, that repulsive movement will never give you back more energy than you spent on pushing them together in the first place. And the same is true if you use attractive force instead of repulsion. Every bit of energy you get from allowing the magnets to push/pull on each other, must be paid for by spending energy on pushing them together/pulling them apart, to get them into that position.
TL;DR: Magnetic forces can store potential energy, but they can’t give you energy for free.
(edit: removed a paragraph about a math topic called “conservative fields,” because some details were potentially misleading/not correct in the most technical sense.)
There is no way to arrange magnets in a way that they don’t cancel the motion they create out. Yes you can offset two magnets and as they pull towards each other they will induce motion, but you can’t control the direction towards which they’re attracting each other, meaning that as the moving magnet rushes towards the stationary magnet and goes past it, suddenly the same force that was accelerating it is now pulling it back and decelerating it.
Even gravity, which can in many ways be compared to magnets though the scales are vastly different, cannot induce perpetual motion, not truly. Yes bodies can orbit each other for billions of years, but no orbit is perfectly stable. They all eventually decay and the bodies come together, just like two magnets in a vaccuum would orbiting each other primarily due to magnetic force with no other force acting on them, which cannot really happen.
Because magnets pull (or repel) at all the time, which balances/cancels the forces out. To manipulate/switch their pull periodically (to get uneven forces), you’d need to use electricty to give (some of) them more power, or block them somehow from pulling mechanically (like moving them or putting something between them and the thing that’s being moved — to block the magnetic field).
Which means you’ll be introducing external energy into system, which means it’s not perpetual motion. Which is how electrical engines work. And which are pretty costly in terms of energy you have to add (to get any practical work out).
Also, anything you move with magnets will encounter air resistance and friction and so forth. Which needs extra “kick” to overcome as well. Again, external source of energy, thus not “perpetual”.
Think of a magnet like similar to gravity in a roller coaster.
If you release a cart, it’ll fall from the top of the hill, gaining movement/”energy”, but if it then goes up the next hill it loses energy again, including a bit more from friction. Eventually your cart will come to rest somewhere on the bottom of the track.
Similarly, if you create a nice setup with magnets, the metal will be pulled towards the magnet(down the hill), but then to keep moving will move away from that same magnet again. Losing energy as if you’re going up the hill.
And it turns out that every configuration of magnets and metal and more magnets, is like adding twists and turns and extra hills to your roller coaster.
‘What if i use an extra magnet?’ Is like asking ‘ what if i use an extra downhill?’.
In the end, there is always a setup for your magnets that is like the ‘cart at the bottom of your roller coaster’. To make any movement you need to put extra energy in to push the cart up the hill.
And no matter your starting setup, due to friction you’ll eventually end up in a low energy state, without any speed/energy to get out of it.
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