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En_TioN t1_ja6ou05 wrote

Reply to comment by Flapflapimabird in eli5 perpetual motion is impossible but why haven't we made something that just goes on for a really long time that we then service so it can keep going? by FrozenKyrie

You can build systems where unused power can be returned to the power source - take regenerative braking in EVs for example. This helps prevent the unnecessary loss of power, and can substantially reduce consumption.

However, you will never return 100% of the energy you extracted back to the power source. The energy used for work can't be returned because you just transferred it somewhere else! Plus, you'll lose energy to heat.

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