tom writes:

Sorry, but you are wrong here. As long as there is no load external to
the engine, it's own friction torque will have no external
manifestation. There will be an external torque, momentarily while the
engine is accelerated or de-accelerated.

If you run the engine in zero gravity, does the crankshaft spin while
the engine remains still, or does the engine spin while the crankshaft
remains still, and why?

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