dille71 said:
Thank you for a great reply.
But imo "perpetual motion" is a bad word to use. One could say that water power is perpetual motion, but it require the heat from the sun to work. If the sun was removed the water would stop to circulate.
Same goes for my idea exept that gravity is required. Remove the gravity and it would stop.
Gravity isn't an energy source, though, so it doesn't power something any more than an oscillating spring does. That's why this is perpetual motion: it is extracting energy from where there is no energy to extract.
I read somewhere that the first rule of thermodynamic (conservation of energy) was based on the fact that no one had managed to build a working perpetual motion machine. And nowadays scientists say that perpetual motion can't be retrieved because of that rule...
No. The first law comes from very simple math. Whether it be a spring-mass system, a roller-coaster, or your device, it is a simple matter to add the kinetic energy to the potential energy and see that you always get zero.
Try it. Take an object at height X, and apply Newton's laws of motion to calculate its speed when it hits the ground. Calculate the kinetic energy and potential energy and see if they are equal (and opposite).
I don't really believe in "perpetual motion" but i believe that new ways to extract energy can be found.
Certainly, but the point of the 1st law is that in some situations,
there is no energy to be extracted.
No comments? Is it a too foolish idea? Or is the picture difficult to understand?
I did start to play with the numbers - it isn't hard, it just takes time and I wasn't particularly motivated. What I was finding is that the buoyancy of such a device is highly limited by the fact that water is so much denser than air: bouyancy difference starts off surprisingly small and quickly shrinks to uselessness.
You really should learn to do these calculations yourself, though - this is something most people learn in junior high. For the amount of time you spend thinking and speculating about it, it is all utterly useless if you aren't learning anything. You're just spinning your wheels in place. Perhaps, then,
you should post
your calculations and we'll help you with them.
For starters, you'll need to make some more assumptions about the things you are using. Ie, the cylinder's wall thickness can be ignored if it is neutrally buoyant, but the volume of the weight cannot. Assume constant water depth/pressure along the device (for now...). Try different aspect ratios and see how that affects it.
Lead has a specific gravity of 11.4. Calculate the buoyancy of the cylinder upright and upside down using the following steps:
-Calculate the pressure in the cylinder based on the area and the weight on it.
-Ratio the pressures to the total volume to find the new volume.
-Add the volume of the weight.
-Now you have the new volume and mass (weight) of your device.
Perform the same calculation with the cylinder upside-down.
What you will find is that there is a buoyancy difference, but not that much.
I'm not certain, but I suspect that where you lose your energy is in the rotation: The center of buoyancy and center of gravity are at two different places and the center of gravity moves as the device rotates. So as the cylinder rotates, its potential energy changes and you lose energy (you don't travel the same distance in both directions). That calculation is also very simple though: the center of mass is the geometric center of the weight and the center of buoyancy is the center of the volume (of the cylinder+weight).
