• Question: How Much does the Earth/Sky Weigh?

    Asked by bubulis to Aggelos, Andrew, Eileen, Naomi, Shane on 15 Nov 2012.
    • Photo: Eileen Diskin

      Eileen Diskin answered on 15 Nov 2012:

      Unfortunately, there isn’t a scale big enough to weigh the Earth. So scientists have to do some calculating to try and figure it out by trying to estimate how much some of the different parts weigh. This includes not only the things that live ON the Earth, but also all of the bits that make up the Earth itself – the crust, rock, mantle, and liquid core.

      Altogether, they estimate that its 6.6 SEXTILLION tons! That’s
      6,600,000,000,000,000,000,000 tons, which is a number thats really hard to imagine! (And technically, scientists call this its ‘mass’ – since only things that are measured taking gravity into account are called ‘weights’)

      One cool thing – the weight of tiny little ants on Earth is about equal to the weight of all of the humans on Earth…because there are so so so many of them!!!

      And Earth might need to go on a ‘diet’ one day! Because of different things hitting the Earth (space debris like meteorites and cosmic dust), our Earth is actually gaining mass!!

    • Photo: Shane Bergin

      Shane Bergin answered on 15 Nov 2012:

      I asked my students to work this out the other day (without google). you could do it too

      1. assume the earth is a sphere. it’s diameter is around 12,000km. therefore it’s volume (v=(4/3)pi.r^3) would be around 1×10^21m^3
      2. What’s the earth made out of. Ans= mainly metal
      3. How heavy would 1m^3 of metal be? Well a car is 1.5tonnes (1,500kg) so i guess around 6,000kg.. it’s solid and REALLY hard to lift
      4. therefore if we have 1×10^21 cubic meters each weighing around 6,000 kg, then the earth should weigh ~ 6.2×10^24 kg.
      This compares with the real answer of 5.9×10^24kg… not too bad a guess when you think i just used my head. physicists are always working things like this out.

      you can do some too

      1. How fast does your hair grow in meters/sec?
      2. How many leaves are on a big tree (in the summer)?

    • Photo: Andrew Jackson

      Andrew Jackson answered on 16 Nov 2012:

      A clever way the Earth’s mass (weight) was measured around the year 1800 by scientists was to use some string, a weight, some maths and a large mountain! Since all objects with mass have an effect of gravity, the weight on the end of the string (a pendulum) was pulled towards the mountain very very slightly. By measuring this movement, and doing some pretty basic maths, the scientists were able to guess at the density of the earth and hence its mass. They got very close to the right answer with this simple experiment.

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