Where does the energy come from?

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The discussion centers on the source of kinetic energy in iron when placed near a magnet, explaining that the iron possesses potential energy in the magnetic field, which converts to kinetic energy upon release. The principle of conservation of energy is emphasized, highlighting that the total energy, comprising kinetic and potential energy, remains constant. Clarifications are made regarding the energy dynamics between permanent magnets and ferromagnetic materials, likening it to electrostatics. The initial assertion about energy sources is confirmed as correct, countering any doubts raised. Understanding these energy interactions is crucial in physics.
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put a iron beside a magnet,then we konw the iron would be attracted toward the magnet.but where does the kinetic energy of the iron come from?
 
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The iron is in a magnetic field, hence it has potential energy due to its position. This becomes KE when the iron is released. The total energy, KE+PE, is conserved.
 
Tomsk said:
Actually, I just read this thread: https://www.physicsforums.com/showthread.php?t=130549. Looks like I'm wrong then...:rolleyes:
You are now wrong. You were right the first time. For a permanent magnet and ferromagnetic iron, the energy considerations do work just as they would in electrostatics with a charge attractilng a polarizable object.
 
Thread 'Question about pressure of a liquid'

Thread 'Question about pressure of a liquid'

I am looking at pressure in liquids and I am testing my idea. The vertical tube is 100m, the contraption is filled with water. The vertical tube is very thin(maybe 1mm^2 cross section). The area of the base is ~100m^2. Will he top half be launched in the air if suddenly it cracked?- assuming its light enough. I want to test my idea that if I had a thin long ruber tube that I lifted up, then the pressure at "red lines" will be high and that the $force = pressure * area$ would be massive...
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