The pull of the Moon and Sun makes gravity wobble slightly during the day
#0016 Science & nature
Fact rank
A
A primary source (GSI) states that tides change gravity; the size of the change agrees between a gravimeter paper and a calculation of the Moon's tidal force
Wow rank
B
Saying scales have tides too is surprising, but the effect is too small to notice
Usefulness
—
A fact worth knowing for its own sake
Verification: Supported by evidence
Rule check: an article whose "why" cannot be written with sources is capped at fact rank B.
AI verification reports the evidence it found; it does not guarantee that a claim is true.
Because of the pull of the Moon and Sun (tides), gravity at the same place changes slightly during the day. The change is only about one to three ten-millionths of gravity (0.1–0.3 milligal), far too small for a household scale.
Why
(No sourced explanation yet.)Evidence
Primary Explanation by GSI. Even at the same place, gravity changes over time with the pull of the Moon and Sun (tides) and crustal movement. Tidal effects start to show in the seventh digit of the gravity value link
Secondary A paper measuring Earth tides for 19 days with a small gravimeter (arXiv). The amplitude varies between about 100 and 300 microgal with the phase of the Moon. The Moon's maximum tidal pull is about 1.1 ten-millionths of gravity (checked by calculation) link
Notes and limits
For an 80 kg person the change in weight is about 0.01–0.02 g. Precise gravimeters see it clearly every day, so gravity surveys subtract the tidal part by calculation. The size depends on latitude and on the phase of the Moon (spring and neap tides), and nearby ocean tides change it by a few percent.
Derivations
Derived from: 体重計の数字は緯度が高いほど大きく出る
Derived facts: —