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Asked by anon-252450 to seancollins, Rosanna on 1 May 2020.
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Rosanna Tilbrook answered on 1 May 2020: last edited 1 May 2020 10:17 am
A lot! Just a smidge under 6,000,000,000,000,000,000,000,000 kilograms.
Also, just to get all technical, this number is Earth’s mass, not weight. They have slightly different definitions. *Mass* is the amount of stuff which makes up an object, and stays constant no matter where you are, whereas *weight* changes with gravity. In other words, weight is a measure of how gravity acts on mass.
For example, a person who weighs 50kg on Earth will only weigh about 8kg on the Moon. This person’s mass hasn’t changed (they haven’t lost parts of their body!), but the strength of the force of gravity on them has changed, as the Moon has a lower gravitational force.
The gravitational forces that act on the Earth are from the Sun and other planets. So you could technically work out the ‘weight’ of the Earth by accounting for all of these, but it wouldn’t really give you a meaningful answer for anything!
Anyway, the upshot of this is: Earth is made up of 6,000,000,000,000,000,000,000,000 kilograms worth of stuff!
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Comments
RobL commented on :
As Roseanna said the Earth has a mass of around 6×10^{24} kg. It is pretty impressive that we have as good a measurement as we do because estimating the mass of the Earth is actually very tricky! Measuring the mass of the Earth is equivalent to measuring the gravitational constant, which due to how weak the gravitational force is, has a huge error bar for a fundamental constant!
The mass of the Earth was measured quite accurately around 250 years ago (in the 1770s) and is now used as a standard unit of mass in astronomy to describe the mass of other planets!
Susan commented on :
Minor comment: measuring the masses of stars in solar masses, and planets in Earth masses, is in fact a bit of a cheat. We know that masses of the panets in Earth masses better than we know them in kilograms, because Newont’s constant G cancels out if you do it that was, and G is one of the least accurately known fundamental constants. (This is because the gravitational force is extremely weak, so it is hard to measure the gravitational force between accurately known masses, which is what you need to do to measure G.)