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A comment on Why are some things darker when wet?. Parent comment

Re:Why are some things darker when wet? by samatman on Thursday January 09, 2020 @03:07PM (#22005073)
Only if the momentum wasn't transferred to the mirror.

Which is, in fact, what happens. Solar sails exploit this fact:

https://en.wikipedia.org/wiki/Solar_sail

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Re:Why are some things darker when wet? by whatshisface on Thursday January 09, 2020 @03:10PM (#22005102)
If momentum was transferred to the mirror then the emitted photon would not have the same momentum as the absorbed photon.
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Re:Why are some things darker when wet? by melon_madness on Thursday January 09, 2020 @05:05PM (#22006398)
Conservation of momentum doesn’t mean that the momentum of the emitted photon has to be equal to that of the absorbed photon. It means the sum of the momentum of the emitted photon and the mirror must equal the momentum of the absorbed photon, assuming the mirror had no momentum to begin with.
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Re:Why are some things darker when wet? by samatman on Thursday January 09, 2020 @03:14PM (#22005151)
> Why the photon is then re-emitted in exactly the same direction that it would have if it was reflected rather than a random direction?

That is, the equal and opposite direction, exactly as predicted by conservation of momentum.

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Re:Why are some things darker when wet? by mr_toad on Thursday January 09, 2020 @08:50PM (#22007782)
Momentum is a vector. The sum of the vectors is preserved.
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