The increased gravitational potential energy comes from the work done by the pressure exerted by the ice on the ball as the water volume expands during freezing. The pressure causes the ball to move upward, thus doing work on the ball and increasing its potential energy with respect to gravity. The work done is equal to the change in potential energy, so the increased potential energy comes from the work done by the pressure.
ImDreamingAwake t1_j6utnl4 wrote
Reply to 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
The increased gravitational potential energy comes from the work done by the pressure exerted by the ice on the ball as the water volume expands during freezing. The pressure causes the ball to move upward, thus doing work on the ball and increasing its potential energy with respect to gravity. The work done is equal to the change in potential energy, so the increased potential energy comes from the work done by the pressure.