A simple experiment that to prove the potential energy is unlimited.

[hansvonlieven]

Thank you,  My proposal is to find a way to kill the gravity of the objects by doing no work. For example:
burn up a pile of wood into ashes.

Zhang Yalin,

You are a complete moron, go home !

Hans von Lieven

[Zhang Yalin]

I feel very sorry to make you so angry. Maybe my English is too poor.

[Zhang Yalin]

If we drop the bottle in the lake which 100 meters in depth, or we use mercury instead of water, It will produce more energy.

[greendoor]

Zhan - you seem to be very young or confused.  What you are suggesting does not make any sense.  Burning something releases chemical energy, but it is not renewable and has no place here. 

You seem to think that bouyancy is a way to cheat gravity and get free energy.  Once you understand how bouyancy works, you will see it is the same power of gravity working, and there is no way to get free lift. 

The only reason a bouyant object rises to the surface is because the fluid around the bouyant object is able to 'fall' down around the bouyant object and 'squeeze' it upwards.  The force comes from gravity - and it is the same downwards vector.  For the float to rise, the fluid has to fall.  And for the float to sink, the fluid has to be displaced.  This takes as much energy to push the float downwards as you could get back when it is squeezed upwards. 

If you think you can cheat the float into sinking with no energy input by changing it's volume - you would be correct.  However - if you then try to inflate the float, to increase it's volume and therefore reduce it's density - you will have to displace the fluid.  In other words, you will have to raise the center of gravity of the fluid as you displace it upwards in the process of expanding the float.  This takes as much energy as you will gain when it float back up - so ultimately this is a lossy sub-unity process.  You will have much less friction loss if you abandon fluid and use heavy masses in air. 

There is no free lunch by using bouyancy.  Never has, never will be.  Despite the many patents for free energy systems based on the idea that bouyant masses rise.  Yes they rise, but that is just as useful as saying heavy masses fall.  Yes they do - but either way, you have to use force to sink the float, or use force to raise the weight.  It's just the same gravity force, just the density of the medium is different.

Having said that - I believe it is possible to extract power from gravity.  It's a similar situation to sailing into the wind.  For thousands of years people uses square sails on boats, and could only sail with the wind.  Eventually they found out how to use triangular sails, and tacking methods that allowed a boat to use the energy of the wind to sail into the wind.  Seems impossible, but it's not.  But there is a trick to doing this.

[Zhang Yalin]

What you said I've known it as well as you, but what I said you seemed misunderstood.