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Weight at night

  1. Sep 9, 2011 #1
    weight is more at night than day. is this right? if not why?
     
  2. jcsd
  3. Sep 9, 2011 #2
    Weight is mass times gravity. Earth's gravity does not change based on the time of day, and the mass will not change unless a reaction takes place, so the weight should not change.
     
  4. Sep 9, 2011 #3

    xts

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    It depends on climate.
    In Northern Europe, weight is more at night, as nighttime we are sleepy and unable to strong effort.
    Contrary, in tropical countries, weight is more during the day - as it is awfully hot, so we are unable to lift even light objects. But, nighttime, the temperature goes bearable, then we may lift much more!
     
  5. Sep 9, 2011 #4
    What??? Weight has a specific physical meaning, and it has nothing to do with how hot you feel.
     
  6. Sep 9, 2011 #5

    berkeman

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    Staff: Mentor

    I believe Himal is just referring to the extra gravitational influence of the sun (and moon). Unfortunately from his terse OP, it is not apparent what he is really asking about.
     
  7. Sep 9, 2011 #6
    Well, your mass stays the same, so it is just a question of whether g is more at night or at daytime.

    I think it is more at daytime because during the day moon is (more) behind the Earth to the Sun and the extra distance towards the moon probably has more effect than the reduced distance to the Sun. This will require a calculation but I'll be kind and let you do it.
     
  8. Sep 9, 2011 #7

    berkeman

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    The bolded part of your post is not true.
     
  9. Sep 9, 2011 #8

    Drakkith

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    You realize the moon orbits the earth and is on the sun side of the earth 50% of the time right?
     
  10. Sep 9, 2011 #9

    Drakkith

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    The net force of gravity, which determines your weight, will vary depending on the relative position of most of the objects in the solar system. (And honestly, the universe) However the force of gravity is so weak from all of these objects that they are not worth bringing up usually. In all everyday situations you will never notice a change in your weight just because the moons is out or not.
     
  11. Sep 9, 2011 #10
    Physicists frequently have no sense of humor. :biggrin:
     
  12. Sep 9, 2011 #11
    If I have water, at different places on earth, that are connected by channels through which water can flow, it seems like I should be able to tell where gravity is the greatest at any given time. Water in the highest gravity regions will be under greater pressure and so will be displaced to the locations where the waters weight (and pressure) are less.

    Unfortunately a lack of international co-operation and funding will likely prevent such a planet wide experiment from ever being constructed.

    :wink:
     
  13. Sep 9, 2011 #12
    yes i am asking about influence of sun and moon. during day attraction of sun and earth are on opposite sides but during night they are in same direction. but what i m confused at is that earth is also being attracted towards sun and that attractional acceleration sums at day to the weight and decrease the weight at night.
    so resultant weight in which case may be greater?
     
  14. Sep 9, 2011 #13
    You weigh the most at low tide.
     
  15. Sep 10, 2011 #14

    D H

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    No, you don't. The tides do not necessarily occur when the Moon is overhead or underfoot. Tides have a phase, and the phase varies (by very much) from place to place.

    You weigh the most at moonrise and moonset.

    Addendum
    The effect is greatest when moonrise/moonset more or less coincide with sunrise or sunset. In other words, full moon or new moon. Even then, the effect is extremely tiny.
     
    Last edited: Sep 10, 2011
  16. Sep 12, 2011 #15
    The gravitational effect of the moon on our small bodies is so small that any variation in our bodies' weight due to the moon would be completely washed out by drinking a glass of water before going to bed. As interesting as the moon's orbit is, the question of cyclical changes in body weight is more a function of eating habits and biology. Now if you are trying to calibrate a super-accurate scale, that is a different question.
     
  17. Sep 12, 2011 #16

    D H

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    Think smaller: It would be washed out by drinking a drop of water before going to bed. The effect is incredibly tiny.
     
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