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  • Tidal forces

    From Luigi Fortunati@21:1/5 to All on Thu Nov 17 10:01:53 2022
    Are tidal forces real or apparent?

    Are tidal forces gravitational forces?

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  • From Sylvia Else@21:1/5 to Luigi Fortunati on Thu Nov 17 18:21:02 2022
    On 17/11/2022 9:01 pm, Luigi Fortunati wrote:
    Are tidal forces real or apparent?


    That's the kind of question that can lead to fisticuffs in otherwise
    polite physics circles.

    They're as real as the gravitational force holding you down to the
    ground, except that some would argue that there's no such thing as a gravitational force, and that what's happening is that you're being
    accelerated by the upwards force from the ground.

    So to avoid physical violence in these situations, you need a very
    precise definition of real versus apparent.

    That said, tidal forces are not as unreal as the Coriolis force that
    appears to be acting on a freely moving object when the observer is in a rotating frame.


    Are tidal forces gravitational forces?

    See above.


    [[Mod. note -- An additional point is that tidal forces can do work:
    https://en.wikipedia.org/wiki/Tidal_power
    -- jt]]

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  • From Luigi Fortunati@21:1/5 to All on Fri Nov 18 08:28:19 2022
    Sylvia Else giovedì 17/11/2022 alle ore 11:21:02 ha scritto:
    On 17/11/2022 9:01 pm, Luigi Fortunati wrote:
    Are tidal forces real or apparent?


    That's the kind of question that can lead to fisticuffs in otherwise
    polite physics circles.

    They're as real as the gravitational force holding you down to the
    ground, except that some would argue that there's no such thing as a gravitational force, and that what's happening is that you're being accelerated by the upwards force from the ground.

    So to avoid physical violence in these situations, you need a very
    precise definition of real versus apparent.

    That said, tidal forces are not as unreal as the Coriolis force that
    appears to be acting on a freely moving object when the observer is in a rotating frame.

    I don't have to give the very precise definition of real strength
    versus apparent strength because it's in all school books.

    That said, the only clear answer to my question is not to say that
    "some would argue" one thing and "others would argue" something else.

    The only clear answer is:
    (1) tidal forces *are* real forces
    or
    (2) tidal forces *are* apparent forces.

    One answer excludes the other.

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  • From Sylvia Else@21:1/5 to Sylvia Else on Fri Nov 18 08:28:19 2022
    On 18/11/2022 1:21 pm, Sylvia Else wrote:
    On 17/11/2022 9:01 pm, Luigi Fortunati wrote:

    [[Mod. note -- An additional point is that tidal forces can do work:
    https://en.wikipedia.org/wiki/Tidal_power
    -- jt]]

    I think the same could be argued for the freely moving object in a
    rotating frame. If you're the rotating observer, then you definitely do
    not want to put your head in the way of a freely moving massive object,
    because it will appear to be doing work on your face. One can then argue
    about what is doing work on what, but the damage to the face will be the
    same.

    Sylvia.

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