Submitted by schematicboy t3_10qtvtb in askscience
AnnaLouise295 t1_j6wl13e wrote
Reply to comment by pblack476 in Suppose I have a container of water with a ball floating on top of it. I put it outside overnight and the water freezes. Since the water's volume increases as it freezes, the ball is raised. Where does the increased gravitational potential energy come from? by schematicboy
It’s been too long since I sat in a physics (or thermodynamics) class to say with certainty, but my guess is that the answer has to do with “types” of energy and sounds something like “some of the thermal potential energy translated to gravitational potential energy”. They alluded to this in the above comments too with the notes on the energy required to move the ball - if the ball wasn’t there, then additional (thermal kinetic?) energy would have been released into the environment.
To say it another way - the gravitational potential energy isn’t the only energy in the system. The total energy of the system after freezing will still be less then before despite the increase in gravitational potential energy due to the decrease in thermal energy.
SynbiosVyse t1_j6wm4fg wrote
You're correct, significant kinetic energy is present in the liquid form and lost during the transition, some of that is converted to potential energy by way of the 9% decrease in the density of the ice compared to liquid water.
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