Physics Moron Needs Your Help

[offmason]

After a boring day of law school classes, I began pondering the ever illusive (and most definitely impossible) perpetual motion machine. Don't ask why, perhaps I was bored.

 

As I am not trained in any form engineering or physics, I have tried brainstorming some possibilities with the only brain I have - one of lackluster quality.

 

In conjuring up one particular idea, I acknowledged that I need a little more information pertaining to automatically retractable cords or wires that recoil upon pressure or certain extension and release. For instance, I have seen a computer mouse with a cord that retracts automatically when it is extended to a certain length. I thought this would be an interesting topic to explore. Let me know if I am barking up the wrong tree.

 

If anyone has any know-how on this particular topic, let me pick your brain!

[farmboy]

Are you asking, would that be a good way to create a perpetual motion machine?

[offmason]

Not sure if that is a solid question, considering that there really isn't a good way to create a perpetual motion machine, as it is essentially impossible.

 

I am interested in finding out how those automatic cord retractors work.

[farmboy]

Yes, it is literally impossible. With the mouse example you put the enrgy in in the first place to stretch the cord out. It is stored as elastic energy in a spring or something, then released to pull the cord back in at a certain point.

[Chriton]

The exchange of Energies from one form to another causes heat to dissapate in the exchange so Perpetul motion would not be possible.

I asked the same question in my Electronics class when I thought that if a Capicitor could be linked with a Coil then they would be self charging but you get a loss of energy in heat so the charge would dissapate...Perhaps with Supper cooled circuits you could, but then it takes energy to Supper cool the circuit

[offmason]

Right, but we can still imagine!

 

My conception: This is probably unworkable in some material respect:

Picture this on paper.

1. Keep the non-electronic/powered cord retractor connected to one end of a cord in the top-left, the other end of the cord connected to a relatively heavy ball.
   
2. Put the ball on the top of a track that angles down at 45 degrees.
   
3. Let the ball go.
   
4. Ball travels from top left to center right.
   
5. Then another track from center right to bottom left. (Picture a ZIG-ZAG)
   
6. At bottom left, the track ends and the ball makes a dead drop - initiating the automatic retractor.
   
7. When it retracts vertically, the ball should (ideally) return to the track, and then gravity takes over again.
   

 

I apologize if I am completely insane for this conception.

Edited February 19, 2010 by offmason

[farmboy]

Wouldn't work unfortunately, the ball wouldn't make it back up.

[offmason]

Why not? Does it depend on the weight? How does a automatically retracting measuring tape?

 

Edited February 19, 2010 by offmason

[farmboy]

Energy would be lost from the system all over the place. Frictional forces in particular will cause energy to leak from the system as the cord extends and the ball rolls. Also I'm not sure about this but it seems that if the ball is heavy enough to pull the string down, it might be too heavy to be pulled back up.

[offmason]

I surmised that the force of gravity would at least counteract or minimize the force of friction depending on the type of material used for the ball or track?

 

The whole point would be to generate sufficient energy with the pulling of the cord. So long as the ball is moving, I would think that energy is being generated.

 

The main issue would be returning the ball to the track, to repeat the process.

[farmboy]

Yeah exactly, theres no problem getting the ball down to the bottom, but it just woudn't make it all the way up to the top. You see basically when the ball is at the top it has a certain amount of gravitational potential energy. As it moves down the track that energy is converted into kinetic energy which in turn is converted into elastic energy in the spring mechanism. Now for the system to work, all of the balls gpe would have to end up as elastic energy in the spring, so that when the spring pulls it back up the ball is returned to its original position and hence original gpe. Unfortunately that will not happen. Not all of the energy will make it to be stored in the spring, some will be lost through heat, friction etc. and so the system will eventually lose its energy.

[offmason]

So is your issue that it will NEVER make it back to the top or that it will only make it to the top a few times?

 

Does the dead drop at the end of the track not make a difference? Doesn't this have something to do with increased velocity at free fall and the associated energy?

Edited February 19, 2010 by offmason

[farmboy]

No way to tell by guessing, it may make it up to the top a few times may never, the important part is that you would never be getting out more energy than you put in.

[offmason]

Was this a piss poor attempt though?

[farmboy]

As you say in your first post, this is literally impossible, so really no idea was ever going to be good lol. I suppose it teaches us something anyway. That what feels right to us, what I suppose you might call our intuition, often lets us down when it comes to matters such as these, highlighting the need for solid empirical data.

[offmason]

Right, but what's the harm in trying to achieve something close to the ideal? Doesn't this all go to the efficiency of producing energy?

 

SORRY TYPO.

Edited February 19, 2010 by offmason

[farmboy]

Right, but that's the harm in trying to achieve something close to the ideal? Doesn't this all go to the efficiency of producing energy?

 

Oh yeah definitely pal, creating more efficent ways of harnesing energy is very lucrative not to mention important

[npts2020]

offmason; If your spring is strong enough to pull the ball back up, it will require input of energy to make the ball go down to begin with. Keep in mind that any rewind spring will take away energy during the downward motion which will never allow your ball to bounce (overcome gravity) back as high as it started. If your spring is perfect, i.e. pulls back with the same energy as required to stretch it, you have essentially a bouncing ball and it will act in a similar manner.

[offmason]

So what about the dead-drop? Does the dead-drop not have any influence on this?

[Sisyphus]

So what about the dead-drop? Does the dead-drop not have any influence on this?

 

What sort of influence do you have in mind?

[UC]

No such thing as a perpetual motion device (unless you'd like to add energy constantly). You could, I suppose picture a ball moving through a perfect vacuum at a constant velocity forever, but what's the point of that. If it interacts with anything, it will lose energy.

[offmason]

I know that there is no such thing as a perpetual motion device. I'm simply floating around some thoughts - albeit dumb thoughts.

 

As the ball rolls down the track, it pulls the cord behind it. Once it leaves the track, the ball makes a dead-drop. I was thinking this dead-drop would provide enough force or energy in the retracting contraption to return the ball to the surface.

 

This way you have some energy being generated by the ball rolling down the track, and then you have the additional energy of the ball in free-fall pulling the cord.

 

UC, I see that you are from New Jersey. As am I! I work out of a law firm in Freehold.

[Sisyphus]

It doesn't matter whether it's rolling or dropping freely. You're still just extracting energy from the decrease in height, i.e. the gravitational potential energy. The maximum useful energy you can get from this process is exactly equal to the minimum energy you would need to lift that weight up through the same height, back to its starting position. In practice, there will always be losses, and the weight will never return to its original height.

[npts2020]

offmason; The problem with using a spring is that it contains no potential energy until you expend energy to wind/compress it. Once you do that you will get all of the energy you put in back out minus friction, inelasticity, etc. It is the same for any system, just sometimes not as easy to visualize.