[JOHN Gamel]

JOHN Gamel  asked the Naked Scientists:
   
Chris,

Just got back from my workout here in Budapest, and - as usual - I listened to your old newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive] the whole time. KEEP UP THE FABULOUS WORK. As I was sweating away, two thoughts came to me that might be of interest to you.

Perhaps you can tell me the fatal flaw in this idea for a perpetual motion machine?

Consider an air-filled cylinder that is closed at one end and contains at the other end a very, very heavy and smooth-fitting cylinder. Now, when you immerse this cylinder in water with the piston end up, the weight of the piston will compress the air, reducing its buoyancy in water. Then, when you turn the cylinder over so the piston end is down, its weight will "pull" on the air, increasing its buoyancy. Finally, mount several of these cylinders on a chain and mount the chain on two sprockets so that as those on one side rise, those on the on the other side descend, while at the top and bottom each cylinder will be rotated 180 degrees.

If this apparatus is immersed in water, why won't the greater buoyancy of the cylinders whose pistons are pointed down cause the chain to turn, thereby generating a perpetual motion machine?

I eagerly await your answer, since this has been puzzling me since my college days.

John Gamel

What do you think?

[syhprum]

Mechanical perpetual motion machines that depend moving balance points, turning things over etc always fail because the power adsorbed by these operations always exceeds the power generated.

[Bored chemist]

Friction in the cylinders, viscosity of the gases and of the water.

[Turveyd]

It will slow down and stop eventually likely on it's side.


It's simply not possible to do.

[Geezer]

I'm confident this will work and I will be happy to help you secure a patent for this wonderful invention. My fees are very reasonable.

To retain my services in this matter, please send a large suitcase stuffed with used pound five pound notes to:

Honest Geezer, Attorney at Law.
C/O HMPS Pentonville

[John Gamel]

I understand that friction of the piston and resistance of the water will tend to slow the machine down, but the fundamental question is this:

Will the cylinder be more buoyant when the heavy piston is pointed down than when it is pointed up?

 If the answer is yes, then (in theory at least) such resistance can be overcome by making the cylinders larger or the pistons heavier.

Problem is, I don't know how to calculate buoyancy in this setting. Any engineers out there want to give it a try?

John Gamel

[Vern]

Will the cylinder be more buoyant when the heavy piston is pointed down than when it is pointed up?

Yes; it will be more buoyant, however, work will be required to reverse the piston. If we disregard all losses, the amount of work required to reverse the piston will exactly equal the amount of work you might get when the piston is pointed down.

[Geezer]

Dearest Mr Gamel,

Pay no attention to these "scientists". They are only trying to steal your brilliant invention.

I am offering a special Halloween discount during October. You will be able to retain my services for a mere suitcase stuffed with used US dollar bills. This is a one time offer that I am sure you will not want to miss.

My associate, Mr Neil, will be happy to conduct the transaction on my behalf at Finsbury Park station. My associate should not be difficult to identify. He will be the rather sheepish individual hanging around on the platform.

Very humbly,

H. Geezer

[neilep]

From the desk of sheepy

Pursuant to the above post and direction from H Geezer Attorney At Law.
Sheepy has asked me to extend his congratulations and invites ewe to meet him at the above locale at 2am. He will be the one wearing............well...he'll be the sheep eating some chips and not looking dodgy at all in his mackintosh and sun glasses reading the Financial Times !

Mr Sheepy invites your attendance and looks forward to conning doing business with ewe.


Secretary to above sheepy.

[The Craftsman]

How about a perpetual fountain?  It's not a machine but it does display perpetual motion.

http://www.youtube.com/watch?v=2Z6UJbwxBZI [nofollow]