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Is Tidal Energy a creation of energy?

  1. Jan 16, 2013 #1
    Is Tidal Energy a "creation" of energy?

    I would like to discuss very basic idea about conversion of energy. Every form of energy we utilize (solar energy, wind energy, geothermal, fossil, hydro, etc) can be traced back to the exhaustion of some kind of energy and mass. Say solar energy, it is only possible due to fusion of H2 molecules into He molecules. Around 600 m metric tonnes/sec of H2 fuse and then the light and heat energy is expelled. Reverse engineering the fossil fuels- are only possible due to anaerobic decomposition of dead organisms; these dead organism are utilized and if they are back-tracked then we find that chemical energy they had posed were derived from plants, animals, which they had received from sun. And talking about hydro-power, the potential energy of the stream is increased due to evaporation of the water(due to wind and thermal energy derived from sun heat) from various sources.
    So Sun is the ultimate source of energy where some mass is at expense every time the energy is transformed. But I wonder where does energy transformation takes place in Tidal Energy. The sheer position of the Earth and the Moon and due to fluidly water. The gravitational force of moon plays a vital role but no energy is expended to "create" the energy. The moon gravitational force is strong enough to lift the tide upto certain meters and then the the tide falls back. Work is done to lift the portion of water but at what expense? No mass of moon is exhaust or any other form of energy at moon is reduced.

    How is it possible to create a energy out of nothing but a mere position of heavenly bodies and fluid? If not then what or which form of energy is being converted from?
  2. jcsd
  3. Jan 16, 2013 #2


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    Re: Is Tidal Energy a "creation" of energy?

    madhur.dev, Welcome to Physics Forums!

    There is no creation of energy out of nothing. The Earth-Moon system give up energy (really small amounts) to tidal friction. See this from Encylopedia Britannica:

    "Tidal friction, in astronomy, strain produced in a celestial body (such as the Earth or Moon) that undergoes cyclic variations in gravitational attraction as it orbits, or is orbited by, a second body. Friction occurs between water tides and sea bottoms, particularly where the sea is relatively shallow, or between parts of the solid crust of planet or satellite that move against each other. Tidal friction on the Earth prevents the tidal bulge, which is raised in Earth’s seas and crust by the Moon’s pull, from staying directly under the Moon. Instead, the bulge is carried out from directly under the Moon by the rotation of the Earth, which spins almost 30 times for every time the Moon revolves in its orbit. The mutual attraction between the Moon and the material in the bulge tends to accelerate the Moon in its orbit, thereby moving the Moon farther from Earth by about three centimeters (1.2 inches) per year, and to slow Earth’s daily rotation by a small fraction of a second per year. Millions of years from now these effects may cause the Earth to keep the same face always turned to a distant Moon and to rotate once in a day about 50 times longer than the present one and equal to the month of that time. This condition probably will not be stable, due to the tidal effects of the Sun on the Earth–Moon system.

    That the Moon keeps the same part of its surface always turned toward Earth is attributed to the past effects of tidal friction in the Moon. The theory of tidal friction was first developed mathematically after 1879 by the English astronomer George Darwin (1845–1912), son of the naturalist Charles Darwin."


    Hope that explains it for you. If not, post your doubts or questions here. Members of Physics Forums are always ready to assist true searchers understand our natural world.

  4. Jan 16, 2013 #3


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    Re: Is Tidal Energy a "creation" of energy?

    As Bobby said. The earth looses energy and perhaps surprisingly the moon actually gains some.

    See also..


  5. Jan 18, 2013 #4
    Re: Is Tidal Energy a "creation" of energy?

    Thank-you Bobbywhy and CWatters,
    I am really grateful for providing me the answers to the question that had been puzzling me since my high school (and it was ignorant of me to not seek the answer from the internet). My friends and I used to discuss about this and confuse ourselves. And now I am happy that I asked it here.
    The reason was en lighting to me and the facts are interesting (namely Moon furthering from Earth by about three cm every year and slowing of earth rotation). And thus, the energy is conserved.
    Thankyou guys, for enlighting me...!! :)
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