• Question: How do we know how much the world weighs?

    Asked by anon-258281 on 8 Jul 2020.
    • Photo: Tiffany Chan

      Tiffany Chan answered on 8 Jul 2020:

      We can’t actually calculate a ‘weight’ as weight is a force that results from the action of gravity on objects (formally, it’s the mass of an object multiplied by the gravitational acceleration, which doesn’t quite work if we’re talking about the planet itself!)

      Instead, we can calculate the Earth’s mass – it’s about 6,000,000, 000,000,000,000,000,000 (6×10^24) kg! Here’s a nice explanation of how that calculation works: https://science.howstuffworks.com/environmental/earth/geophysics/planet-earth-weigh.htm

    • Photo: Kat Hunter

      Kat Hunter answered on 8 Jul 2020:

      Exactly how tiffany explained it! wouldn’t it be great if we had a ginormous scales to put it on?!

      It is Sir Issac Newton’s Law of Universal Gravitation to do this – it tells us that the force of attraction between two objects is proportional the product of their masses divided by the square of the distance between their centres of mass. We assume the centre of the earth is the centre of mass in this case.

    • Photo: Heather Walton

      Heather Walton answered on 9 Jul 2020:

      This really isn’t a helpful answer to this question but the original measurements to estimate the earth’s weight were made on the mountain Schiehallion in Scotland! The mountain was chosen because the scientists thought it was quite round and symmetrical, and they measured how much it attracted a weight on a pendulum to determine its mass.
      https://en.wikipedia.org/wiki/Schiehallion_experiment

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