月と太陽の引力で重力は1日のうちに僅かに揺れる/en

#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

Posted by: Mamechi editors ・ Verified: 2026-10-29 ・ Method: AI + human ・ On Wikipedia?: Not on Wikipedia

AI verification reports the evidence it found; it does not guarantee that a claim is true.

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

It is caused by the pull of the Moon and Sun (tides).

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: —