Why can’t magnets make a perpetual motion machine? (Using magnets to propel a turbine the create energy)


I get that the main reason perpetual motion isn’t possible is because energy loss due to friction, but that’s not the case with magnets (I think?). Why can’t perpetual motion be achieved with magnets? What can’t we make something that spins and creates energy using magnets to propel a turbine?

In: Physics

Because actual power is need to supply the magnets powerful enough to produce usable/practical results.

If you use a magnet to pull one side forward to spin the turbine, at some point it will also pull after the magnet is moving away. At each rotation there would be a slight reduction in speed until it stops due to magnets and friction.

>Why can’t perpetual motion be achieved with magnets? What can’t we make something that spins and creates energy using magnets to propel a turbine?

Sure, you can suspend some magnetic contraption within a vacuum, give it a good flick and it would spin a fair bit. It’ll eventually stop due to manufacturing imperfections and constant interactions with external magnetic fields, but that’ll take some time.

Now how did you plan on taking energy **out** of the system without friction or other magnetic fields? How would this turbine be connected to the spinning device?

In order for a machine to produce energy, the energy needs to come from somewhere. Wherever it’s coming from, it’ll eventually run out.

A perpetual motion machine needs to produce energy without that energy coming *from* anywhere, which is nonsense.

A magnet pulls in one direction. How are you going to get it to produce a spinning motion? Sure, you can *start* something spinning by pulling with a magnet, but once the thing you’re pulling on has spun past the magnet’s position, the magnetic pull is now slowing it down. The only way you can maintain the spin is either to switch the magnet on and off (which means a powered magnet, which means you have to supply power) or else move the magnet as well (which requires power).

> but that’s not the case with magnets (I think?)

There is still friction with magnets, there’s just much less of it because the objects are effectively very smooth (because they only feel irregularities in each others’ magnetic fields, not in their surface shape). The two objects still interact in ways that transfer energy of motion into the random jiggling of higher temperature, just not as much as if they were in (what you normally think of as) physical contact.

No matter how you arrange the magnets, and even if you get rid of friction (which you can in theory but not in practice), and even if all the magnets are perfectly uniform so there’s no irregularities in the fields or anything that causes waste…it still won’t work.

Like /u/d2factotum says, magnets only pull (or only push if you turn them around). You can create an unbalanced setup where the magnets want to turn the turbine *at first* but if you do that there will be an orientation where the turbine is stable…it’ll turn to that position then stop. And if you create a perfectly balanced setup then there’s nothing to turn it in the first place.

If you crank through all the math of all the magnets pushing and pulling on all the different parts of the turbine, you’ll discover that the total energy output in a full rotation is…zero. It doesn’t matter how you arrange anything, it’ll always come out to zero, so you can never continue to extract energy by it spinning forever.

A magnet is a configuration of material that causes nearby objects to interact in a certain way. This has little to do with energy, except that it takes energy to change configuration, to make a magnet.

A magnet is like a hole on the ground with sloped sides. Magnetically attracted things are like round objects. These will roll downhill, like certain metals stick to magnets. But you have to put energy in to set the objects up on the hill in the first place. So you don’t get any free energy out.

If you could find an infinitely deep hole, or one that mysteriously never fills, and an infinite number of dense objects to roll into it, you could make infinite energy. Just tie a string to each object and wrap the other end around a generator, let the object roll down. Repeat. Same for a magnet. Infinitely large, infinite number of iron balls tied to strings. But you see how this can’t happen with magnets and for very similar reasons it wouldn’t work with a hole in the ground.

The mystery of magnetism comes from being unable to sense the cause of magnetic behavior. At the deepest level, things interact differently depending on their configuration all the time and it doesn’t wow us because the causes are easy to see.

If you somehow lacked the ability to comprehend roundness, you might believe round things are more energetic than other shapes, or capable of generating power, since round things roll downhill. But we know round things just do that because of the way their configuration interacts with the environment and there’s no mystery there. Magnets are the same way.

Magnets have other interesting properties of course, but still, it all comes down to configuration and the resulting ways things interact. Nothing about magnets generates power. They’re a configuration, like a shape, of stuff.