Semicircular Permanent Magnet Rail Gun - continuous motion?

[aeroseek]

Doubtless you are all familiar with a rail gun made by using permanent magnets.

An example is given here:

http://sci-toys.com/scitoys/scitoys/magnets/gauss.html

Assuming the railgun could me made curved, won't it be possible to build a curved track to transport the projectile - assume a steel ball on a track - to the starting point so continuous motion of the steel ball is achieved?

This is not perpetual motion since the magnet would eventually lose their strength.

 

[jambaugh]

Nope, look carefully at the configuration before and after. You have to reset it which require energy input.

 

[aeroseek]

Well I am open to proof that it cannot work, however I am not sure about the reason for saying it cannot work.

To simplify matters, just imagine a permanent magnet rail gun://////////
0======
\\\\\\\\\\

The steel ball is place at the start of the gun with a velocity zero or greater at the start of the rail gun. Due to the forces of the magnets the steel ball moves down the rail in the diagram to the right.

//////////
======0=
\\\\\\\\\\//////////
======= 0
\\\\\\\\\\

Something similar has been shown on Discovery TV, and there is no question that it works.

There are two questions that can be asked here:

1. Can the ball, possessing a velocity, have sufficient momentum to be directed back to the starting point using a circular track?

In the demonstrations I have seen on You Tube the projectile does pick up substantial speed using the rail gun, so this should be possible.

2. If the steel ball is re-routed to the start of the rail gun, will it be accelerated down the rails once again?

I cannot at present see a reason why the answers to both these questions should be in the negative.

 

[A.T.]

Well I am open to proof that it cannot work,

The attraction between the balls and magnets is like a conservative field. You can convert potential into kinetic energy and vice versa, but their sum is at best constant, and dissipates through losses in real life.

You should ask yourself: If all you need is a couple of magnets and steel balls, why hasn't anybody build a working circular one yet?

 

[davenn]

Well I am open to proof that it cannot work, however I am not sure about the reason for saying it cannot work.

....

I guess you didn't read to the bottom of the page on the link you gave ??

Why a circular track will not be a perpetual motion device

I have been getting a lot of mail asking what would happen if we made the track circular. Would we get free energy? Would the balls keep accelerating forever?

I have been tempted to reply with the famous quote: "There are two kinds of people in the world -- those who understand the second law of thermodynamics, and those who don't".

However, I am not the kind of person to leave an inquiring mind unsatisfied, and it is more productive (and kind) to explain in a little more depth what is going on.

Suppose you made a circular track, and put two balls after each magnet. When the last ball is released, it encounters a magnet that has two balls at the ground state. There is no energy to be had from this magnet. The ball just bounces back.

Now suppose you had placed three balls after each magnet. When the last ball is released, it hits a ball that is 5/8ths inch from the magnet. It has not gained much momentum, because most of the momentum gained is in the last half inch as the magnet pulls much stronger on things that are closer. But the ball has enough energy from previous accelerations to release the next ball. However, that ball has less energy than the ball that caused it to release. It may have enough energy to release another ball or two, but each ball that is released has less energy than before, and eventually the chain stops.

You can show by inductive logic that no matter how many balls you stack in front of each magnet, eventually the system stops.

To estimate the losses due to heating the balls as they compress when hit, consider a plastic tube standing upright on a table. Place one steel ball at the bottom of the tube. Now drop another ball into the tube, so it hits the ball at the bottom, and bounces back up.

Now measure how high the ball bounced. If it bounces halfway back up, the losses are 50%. Perform the experiment for yourself with the balls from the Gauss Rifle. How high does your ball bounce? Send me mail with your results.

cheers
Dave

 

[davenn]

This is not perpetual motion since the magnet would eventually lose their strength.

but that wouldn't happen for zillions of years, so in reality ( well your reality anyway)
you are claiming perpetual motion

and as such, any further discussion is against forum rules
so expect this thread to be closed


cheers
Dave

 

[aeroseek]

Sure I read that, but that is not a suitable example regrettably. The system I am describing does not use several balls and collisions to work - it is a simple magnetic rail gun as shown here:

www.youtube.com/watch?v=Vo2-Qb3fUYs

 

[aeroseek]

OK OK, before you close the forum - imagine an electromagnetically driven rail gun - energy is input from a battery into two electromagnets that accelerate a steel ball on a track. Now will this motion continue as long as the
* electro magnets * are switched on?

http://en.wikipedia.org/wiki/File:Rail_Gun.png

 

[A.T.]

but that wouldn't happen for zillions of years, so in reality ( well your reality anyway)

I think that misses the point. I'm not sure that "magnet losing it's strength" constitutes any source of energy, no matter how negligible. Isn't the magnetized state of lower potential energy than the demagnetized? It would seem to me that you have to put (thermal) energy into the magnet to demagnetize it.

 

[A.T.]

Sure I read that, but that is not a suitable example regrettably. The system I am describing does not use several balls and collisions to work - it is a simple magnetic rail gun as shown here:

www.youtube.com/watch?v=Vo2-Qb3fUYs

This argument in post #4 still applies here.

 

[davenn]

I think that misses the point. I'm not sure that "magnet losing it's strength" constitutes any source of energy, not matter how negligible. Isn't the magnetized state of lower potential energy than the magnetized? It would seem to me that you have to put (thermal) energy into the magnet to demagnetize it.

yeah true

 

[CWatters]

For the purposes of this thread a magnetic field can be considered conservative...http://en.m.wikipedia.org/wiki/Conservative_force

Eg if you move in a circle no work is done. Basically you can't ever "close the loop" and get the energy out that is needed to overcome losses.

Hasn't stopped lots of misguided people trying and posting their efforts and fakes on YouTube.

 

[Doc Al]

OK, time to close this thread. Discussions of perpetual motion schemes are not permitted.