月と太陽の引力で重力は1日のうちに僅かに揺れる/enのソースを表示

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{{豆知識
|番号=0016
|投稿者=まめち編集部
|本文=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.
|なぜ=It is caused by the pull of the Moon and Sun (tides).
|ジャンル=科学・自然
|ファクト度=A
|ファクト度の根拠=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
|ネタ度=B
|ネタ度の根拠=Saying scales have tides too is surprising, but the effect is too small to notice
|便利度=該当なし
|便利度の根拠=A fact worth knowing for its own sake
|検証ステータス=根拠あり
|根拠1URL=https://www.gsi.go.jp/buturisokuchi/grageo_gravity
|根拠1要約=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
|根拠1格付け=一次
|根拠2URL=https://arxiv.org/pdf/2109.13715
|根拠2要約=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)
|根拠2格付け=二次
|補足=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.
|検証日時=2026-10-29
|検証方式=AI＋人
|本家既出チェック=未掲載
|派生元=体重計の数字は緯度が高いほど大きく出る
}}