What is the source of energy responsible for Earth movements (rotation, translation, etc.)?
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4$\begingroup$ Why would a source of energy be required for non-accelerating movements? $\endgroup$– JMacMay 22, 2019 at 18:51
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$\begingroup$ @JMac Neither the revolution of the Earth around the Sun, nor the rotation of the Earth on its axis, are non-accelerating movements. (Nevertheless, neither needs an energy source to keep them going.) $\endgroup$– G. SmithMay 22, 2019 at 19:32
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1 Answer
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Energy is not required for movement. You only need energy for changes in movement, such as some accelerations.
For the way we usually think about the Earth's movements, there is no energy source because it's already in motion. Orbital motion, in particular, is a kind which requires no additional energy... kind of like how it takes no additional energy to keep moving when you're slipping on ice.
If you want to get deeper than that, the energy which got the Earth moving in its current way did indeed come from somewhere. It came from the gravitational potential energy of dust as that dust coalesced into clumps, and later into planets. But we rarely choose to think that far in the past. Usually we say that the Earth has its kinetic energy, and the path of its orbit does not change that energy.
answered May 22, 2019 at 19:28
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1$\begingroup$ Minor note (to v1): the path of Earth's orbit does change its kinetic energy, but only to the extent that Earth's orbit is non-circular, and in a periodic way. $\endgroup$– rob ♦May 22, 2019 at 19:38
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1$\begingroup$ @rob Good point. There is some transfer of kinetic energy to potential energy as the Earth moves a little further from the sun in its orbit, and a transfer back as the Earth moves closer. Curse you, reality, and your little-yet-important nuances! $\endgroup$ May 22, 2019 at 19:40
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$\begingroup$ Please, correct me if I understood it wrong: Earth "has" a constant amount of mechanical energy (Potencial + Kinetic). It moves in a certain trajectory on the deformed space created by the sun. In this movement, potential and kinetic energies change but are balanced, keeping mechanical energy constant forever and ever. Am I right? $\endgroup$ May 23, 2019 at 14:48
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$\begingroup$ @RobertoDiasAlgarte Correct, within reason (drag against the handful of hydrogen atoms in space, etc.) Its the same kind of balance we see with a pendulum, where the energy is all potential at the highest point, that energy transfers to kinetic as it races the the bottom, and then back as it reaches the other high point. The only difference is that it's really easy to intuitively see that in a pendulum, and takes a bit more digging to see it in orbital mechanics. $\endgroup$ May 23, 2019 at 14:51
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$\begingroup$ I knew it !!! I refused to believe that there was no friction at all and the movement was free from any dissipation! $\endgroup$ May 23, 2019 at 14:58