Thermodynamics question

[Tres Juicy]

Hi all,

 

I've just been reading some posts on here about perpetual motion and magnetism (I know...).

 

and the thought occured to me: why can magnets not be considered an outside source of power?

 

like a water wheel uses water to turn the wheel, why can magnetism not be used the same way? (a constant downward force on one side of the wheel)

 

if the magnet provides the power (seperate from the system) surely this doesn't break the rule? or does it? if it does, why?

 

It may look like a stupid question, but its hurting my brain...

 

Thanks,

 

Alan

[CaptainPanic]

Water in a water wheel falls down, loses potential energy, and some of that potential energy becomes kinetic energy in the wheel. The kinetic energy can then for example turn a generator making electric energy.

In a magnet, it costs energy to make something move towards a magnet, or to remove it from it. To move a magnet in a magnetic field takes energy... this is similar to the potential energy. For the time being, I'll just call it 'potential energy' as well.

 

But the crucial difference between magnets and water is that you have a continuous supply of water, which is always falling down. Mother nature provides rain (through evaporation powered by the sun's nuclear fusion reactions).

If you have a continuous supply of fresh magnets which always "fall down" towards the opposite poles in the right orientation, then you can extract that 'potential energy'. But if you have only a couple of magnets, then this will stop as soon as they are in their lowest energy position.

Similarly, if you have a limited amount of water, then a water wheel is rather pointless. Once all the water is down, it stops.

[Tres Juicy]

Water in a water wheel falls down, loses potential energy, and some of that potential energy becomes kinetic energy in the wheel. The kinetic energy can then for example turn a generator making electric energy.

In a magnet, it costs energy to make something move towards a magnet, or to remove it from it. To move a magnet in a magnetic field takes energy... this is similar to the potential energy. For the time being, I'll just call it 'potential energy' as well.

 

But the crucial difference between magnets and water is that you have a continuous supply of water, which is always falling down. Mother nature provides rain (through evaporation powered by the sun's nuclear fusion reactions).

If you have a continuous supply of fresh magnets which always "fall down" towards the opposite poles in the right orientation, then you can extract that 'potential energy'. But if you have only a couple of magnets, then this will stop as soon as they are in their lowest energy position.

Similarly, if you have a limited amount of water, then a water wheel is rather pointless. Once all the water is down, it stops.

 

Ok,

 

Picture a wheel with arms extending out from the center at regular intervals each with a magnet on the end of each one facing north side up.

 

Each arm has a "hinge" in the middle that allows it to bend 80 degrees from straight to the left.

 

The wheel turns in such a way that the arms on one side are straightend by gravity and the other side is bent.

 

near the top of the wheel there will be a point at which the arm/s will "fall" into the straight position

 

At the point at which gravity straightens the arms there is a magnet placed above the rotating magnets facing north down so that the rotating magnets "fall" through the field into the repelling N/N field creating enough "push" to let gravity drop the next one into the field and so on.

 

A thick piece of ferromagnetic material can be used to seperate the rotating magnets from the static one to prevent them from reppeling each other until they have reached the right position.

 

Gravity and magnetism both working to "push" one side of the wheel with thermodynamics still in tact

 

 

Why does this not work??

[Dekan]

A interesting and ingenious mechanism! But - it has a wheel. This must have an axle, which turns round, in some kind of support. The turning will make friction between the axle and its support.

 

Similarly, the arms have hinges. When the hinges turn, there'll be more friction.

 

So won't this friction, eventually bring the mechanism to a stop?

[Tres Juicy]

A interesting and ingenious mechanism! But - it has a wheel. This must have an axle, which turns round, in some kind of support. The turning will make friction between the axle and its support.

 

Similarly, the arms have hinges. When the hinges turn, there'll be more friction.

 

So won't this friction, eventually bring the mechanism to a stop?

 

 

obviously the forces involved need to overcome friction, there are no frictionless bearings

 

its just something that I thought of while reading the threads about it...

 

what I thought was that gravity on its own will clearly fail, so will magnetism but together they might work

 

gravity cant turn the wheel, but it can drop the arms into place (this takes the problem of friction in the hinges out) so that the magnet can nudge it round ready to repeat. the more I think about it, the more valid it seems.

 

Give me a few weeks and I will have cracked it!

 

Going back to the OP...

 

Does/would this leave thermodynamics in tact??

 

Its not truly a closed system (having external force applied by the top magnet)

 

Or am I missing something?

[CaptainPanic]

You've fallen for the trap of making your contraption complicated enough that you don't understand why it doesn't work

 

I've done the same many times (that's just another way of saying that there's no shame in doing that).

 

See if you can make an energy balance. What has how much energy during 1 revolution of that wheel? (Choose several logical positions of the wheel where stuff is about to happen, and right after it happened). Make sure to describe everything...

 

If more energy comes into your system, make sure to describe where it came from.

 

Ok,

 

Picture a wheel with arms extending out from the center at regular intervals each with a magnet on the end of each one facing north side up.

 

Each arm has a "hinge" in the middle that allows it to bend 80 degrees from straight to the left.

 

The wheel turns in such a way that the arms on one side are straightend by gravity and the other side is bent.

 

near the top of the wheel there will be a point at which the arm/s will "fall" into the straight position

 

At the point at which gravity straightens the arms there is a magnet placed above the rotating magnets facing north down so that the rotating magnets "fall" through the field into the repelling N/N field creating enough "push" to let gravity drop the next one into the field and so on.

And what got you the energy to first push the magnets into that unfavorable position? If the force of the field is strong enough to move the whole contraption, then there is a chance that the arms wouldn't fall into that field at all... but instead, the static and moving magnets would be repelled so strongly to make them hover somewhere halfway.

 

A thick piece of ferromagnetic material can be used to seperate the rotating magnets from the static one to prevent them from reppeling each other until they have reached the right position.

 

Gravity and magnetism both working to "push" one side of the wheel with thermodynamics still in tact

 

 

Why does this not work??

Well, you need to put in an equal amount of work to push those magnets into that field as you will get out when they push themselves out. Likewise, you put in an equal amount of work to move something up against gravity as you get out when it comes back down. To make the geometry more complicated only moves the problem around, but won't change the fundamental issue that you need to spend energy to push similar poles of magnets towards each other, so you can get out the same (or actually a little bit less). There is no input of energy. You lose a little to all kinds of frictions, and that's it.

 

There is a way around this problem... you can use electromagnets, which you can turn on and off when you like. And that, ladies and gentlemen, is called the electromotor

[Tres Juicy]

You've fallen for the trap of making your contraption complicated enough that you don't understand why it doesn't work

 

I've done the same many times (that's just another way of saying that there's no shame in doing that).

 

See if you can make an energy balance. What has how much energy during 1 revolution of that wheel? (Choose several logical positions of the wheel where stuff is about to happen, and right after it happened). Make sure to describe everything...

 

If more energy comes into your system, make sure to describe where it came from.

 

 

And what got you the energy to first push the magnets into that unfavorable position? If the force of the field is strong enough to move the whole contraption, then there is a chance that the arms wouldn't fall into that field at all... but instead, the static and moving magnets would be repelled so strongly to make them hover somewhere halfway.

 

 

Well, you need to put in an equal amount of work to push those magnets into that field as you will get out when they push themselves out. Likewise, you put in an equal amount of work to move something up against gravity as you get out when it comes back down. To make the geometry more complicated only moves the problem around, but won't change the fundamental issue that you need to spend energy to push similar poles of magnets towards each other, so you can get out the same (or actually a little bit less). There is no input of energy. You lose a little to all kinds of frictions, and that's it.

 

There is a way around this problem... you can use electromagnets, which you can turn on and off when you like. And that, ladies and gentlemen, is called the electromotor

 

 

Hi,

 

I understand what you're saying, but....

 

"If the force of the field is strong enough to move the whole contraption, then there is a chance that the arms wouldn't fall into that field at all... but instead, the static and moving magnets would be repelled so strongly to make them hover somewhere halfway. "

 

Thats why I have included the ferromagnetic "shield" (yes, I've given it a cool name so that appears more credible - you want to like it don't you?), this will attract the moving magnet and to some extent negate the repulsion of the oposing magnet until it is in the correct position.

 

The reason I have added hinged arms is to increase acceleration (due to gravity) through the part of the field that is likely to cause them to "hover" mid way.

 

The aim being to have them travelling at their maximum speed through the "sticky patch"

 

In short, I'm trying to make it relatively easy to get into the unfavourable position (and once they're in, they will be immediately forced out, dragging the next one in ad infinitum...)

 

Dont get me wrong, I thought of this this afternoon at work...

 

I'm just curious as to whether magnetic power breaks the 2nd/3rd LoT, the way I see it magnets are almost like "stored" energy and it seems to be reasonable to divise a way to use that energy

 

Thanks for all the feedback though, keep it coming

Edited December 5, 2011 by Tres Juicy

[CaptainPanic]

[/b]Thats why I have included the ferromagnetic "shield" (yes, I've given it a cool name so that appears more credible - you want to like it don't you?), this will attract the moving magnet and to some extent negate the repulsion of the oposing magnet until it is in the correct position.

If you need to climb to the top of a mountain, then you can do this the long way using a long and scenic winding road, or in a ski lift, or if you like, but helicopter or catapult... but in the end, you still end up on the top of the mountain, and your potential energy will have increased by exactly the same amount (of course, we're assuming you started in the same place).

 

It is true that the methods to get to the top might waste more or less energy (that's the 'friction'). But the thermodynamic result is exactly the same.

 

So, you might use a ferromagnetic shield... but as soon as the moving magnet gets into the field of the other magnet, it will still need to overcome the same repulsion (although, along a shorter path).

 

What you're suggesting is that it would take less increase in potential energy if you climb a mountain from the steep side, and more if you take the easy side, but in fact it is the same.

[Tres Juicy]

If you need to climb to the top of a mountain, then you can do this the long way using a long and scenic winding road, or in a ski lift, or if you like, but helicopter or catapult... but in the end, you still end up on the top of the mountain, and your potential energy will have increased by exactly the same amount (of course, we're assuming you started in the same place).

 

It is true that the methods to get to the top might waste more or less energy (that's the 'friction'). But the thermodynamic result is exactly the same.

 

So, you might use a ferromagnetic shield... but as soon as the moving magnet gets into the field of the other magnet, it will still need to overcome the same repulsion (although, along a shorter path).

 

What you're suggesting is that it would take less increase in potential energy if you climb a mountain from the steep side, and more if you take the easy side, but in fact it is the same.

 

No, what I'm suggesting is an imbalance of force.

 

The point where it would encounter resistence is the point where the the arm extends, so gravity does the work of pushing it into the field and it is positioned so that as soon as it does meet resistence there is only one direction that force/resistence can push it (down).

 

By shielding the field on one side I'm trying to make it so that entry to the repulsive field is in a place where the natural rotation (coupled with the "drop" of the arm) will give enough momentum to make it easy to get to a position where suddenly the repulsive force is large enough to push it downwards to a point where it exits the field and drops the next one in.

 

I understand your mountain analogy but think of the fixed magnet as a fast running tap, there is an external force acting upon the wheel causing rotation

[mississippichem]

If you need to climb to the top of a mountain, then you can do this the long way using a long and scenic winding road, or in a ski lift, or if you like, but helicopter or catapult... but in the end, you still end up on the top of the mountain, and your potential energy will have increased by exactly the same amount (of course, we're assuming you started in the same place).

 

It is true that the methods to get to the top might waste more or less energy (that's the 'friction'). But the thermodynamic result is exactly the same.

 

So, you might use a ferromagnetic shield... but as soon as the moving magnet gets into the field of the other magnet, it will still need to overcome the same repulsion (although, along a shorter path).

 

What you're suggesting is that it would take less increase in potential energy if you climb a mountain from the steep side, and more if you take the easy side, but in fact it is the same.

 

Just a rephrase to add to an already succinct explanation:

 

The work done is path dependent but the change in potential energy is not!

 

This is a major source of confusion among students in thermodynamics courses and even among professionals sometimes when the situation becomes significantly more complicated.

 

An easy pit to fall into for sure.

[swansont]

I'm just curious as to whether magnetic power breaks the 2nd/3rd LoT, the way I see it magnets are almost like "stored" energy and it seems to be reasonable to divise a way to use that energy

 

No, they don't break any thermodynamics laws. The reason they seem tempting is that magnets ultimately do no work (they induce an electric field which does) so it acts as a mechanism for converting mechanical to electrical and back, which means what you are used to seeing as lots of energy is really the external input, not the energy stored in the magnet.

[CaptainPanic]

I understand your mountain analogy but think of the fixed magnet as a fast running tap, there is an external force acting upon the wheel causing rotation

There's a difference between a bucket of water, and a running tap. One is a limited amount of water, the other is a flow (continuous, and indefinite). Are you sure it's like a running tap?

 

Maybe you care to explain your analogy of the magnet being like a running tap? Where does a magnet get continuously fresh energy, or fresh something else from?

 

A running tap gets new water all the time, and that water is being pushed into the water system by pumps at the treatment facility. Where does the magnet get something new from? As far as I see it, a magnet is a static object, and unless something else acts in its surroundings, it will not do anything. It's not 'running'... but maybe you care to explain, so that we can figure out what you don't understand.

 

Yep, I'm inviting you to make a mistake - all with the purpose of learning, so don't worry, we won't bite (hard).

[Tres Juicy]

No, they don't break any thermodynamics laws. The reason they seem tempting is that magnets ultimately do no work (they induce an electric field which does) so it acts as a mechanism for converting mechanical to electrical and back, which means what you are used to seeing as lots of energy is really the external input, not the energy stored in the magnet.

 

 

Ok, so if we can use this force in one direction, surely the water wheel principle can be used to push one side of a wheel downwards indefinitely (whether the power is coming from the magnet itself or the field it generates)

 

and this will not break thermodynamics in any.

 

again, if you replace the top magnet with a running tap there would certainly be no objection from anyone and the wheel would turn as long as the water was running.

 

so provided I can shape the field created by the magnet (or alter the path of the other one) to make it a "downwards only" force it should work...

 

 

I think I need to build it.... I am a resonable person and I know it shouldn't work, but I can't get it out of my head now.

 

I need to prove myself wrong I think, it should be fun failing anyway and I'll probably learn a thing or two about why I'm an idiot

 

 

Just out of interest, does anyone agree that if the shape of field could be modified to produce long thin lines of force eminating from the poles, it could then be made to work?

 

Thanks,

 

Alan

[CaptainPanic]

so provided I can shape the field created by the magnet (or alter the path of the other one) to make it a "downwards only" force it should work...

A magnet has two ends, north and south... and the field lines will curve, and some of them will certainly be pointing up as well.

 

by the time you enter the area with the field lines pointing down, you will certainly have crossed some lines pointing in the wrong direction already.

 

Do yourself a favor, and make a drawing first. I get the idea that you don't get the field lines of the magnets right, so make sure to show that to someone who can point out your error. It might save you some time.

 

On the other hand, building something is always good... and whether it works or not, will be a nice lesson, and probably good fun. Good luck!

[Tres Juicy]

I am aware that the lines of force curve back around, but I'm trying to negate their effects in a portion of the field

[CaptainPanic]

I am aware that the lines of force curve back around, but I'm trying to negate their effects in a portion of the field

You cannot break a line. You can only redirect it. Placing a ferromagnetic thingy will only move the line somewhere else, but it won't break it.

[Tres Juicy]

You cannot break a line. You can only redirect it. Placing a ferromagnetic thingy will only move the line somewhere else, but it won't break it.

 

 

I dont want to break it, only to redirect it somewhere it will have a useful effect

[swansont]

I dont want to break it, only to redirect it somewhere it will have a useful effect

 

You can't force an asymmetry that will let you extract net work.

[Tres Juicy]

You can't force an asymmetry that will let you extract net work.

 

 

Imagine a conveyor belt carrying a stream of magnets to a destination, at the end of the belt they must be removed into a bucket.

 

All the magnets on the belt are aligned so that their N points in the same direction (lets say East). At the end of the belt there is a very large magnet with its N pole facing West.

 

This act to push the smaller ones off the belt and into the bucket (ignoring the fact that they would just spin around and stick to the big one, lets imagine they are held somehow).

 

Would this be considered Net Work?

 

The large magnet has moved the smaller ones by X distance in Y amount of time.

 

Is that not work? Object A goes to position B at speed C, thus work has been done

Edited December 6, 2011 by Tres Juicy

[swansont]

Imagine a conveyor belt carrying a stream of magnets to a destination, at the end of the belt they must be removed into a bucket.

 

All the magnets on the belt are aligned so that their N points in the same direction (lets say East). At the end of the belt there is a very large magnet with its N pole facing West.

 

This act to push the smaller ones off the belt and into the bucket (ignoring the fact that they would just spin around and stick to the big one, lets imagine they are held somehow).

 

Would this be considered Net Work?

 

The large magnet has moved the smaller ones by X distance in Y amount of time.

 

Is that not work? Object A goes to position B at speed C, thus work has been done

 

By net work I mean through a complete cycle. If you return to the starting point, the energy will not have changed. You can always find ways to set up a system that has potential energy and extract that potential energy, but that requires work to configure.

[Tres Juicy]

By net work I mean through a complete cycle. If you return to the starting point, the energy will not have changed. You can always find ways to set up a system that has potential energy and extract that potential energy, but that requires work to configure.

 

 

I think I can make this work...

 

You'll all get mentioned at my Nobel acceptence (probably as "The Nay-Sayers")

 

I have 20 or so big neodymium magnets, a tube of glue and some Lego, that will keep me busy for half an hour.