• Question: how many grains of rice would it take to create a loop around the sun?

    Asked by n00b to Chris, Eva, Michael, Paddy, Philip on 14 Jun 2011.
    • Photo: Chris Jordan

      Chris Jordan answered on 14 Jun 2011:

      It depend how far out the loop is.
      If you want to make a loop as far out as we are (ie earth’s orbit round the SUN) – we are around 150 million kms from the sun – so our orbit is 2 x PI x R which is approx 1000 million kms long. I guess a big grain of rice is 1 cm (10 mm) so you’d need 100 grains for a metre and 100,000 grains for a km.
      Which gives 100,000 x 1000 million grains. We’d write that as 10^14 (ie 1 plus 14 zeros)

    • Photo: Michael Wharmby

      Michael Wharmby answered on 14 Jun 2011:

      Taking the same approach as Chris, but with short grain rice (mmm, rice pudding…) and assuming you mean around the sun itself, rather than out at the Earth:
      Radius of the sun: 695500 km
      One short grain rice grain: 4 mm = 0.000004 km
      So the circumference of the sun is 2 * pi * r = 2 * 3.14159… * 695500 km = 4369955 km
      No. grains of rice: 4369955/0.000004 = 1.09 trillion (1.09×10^12 – 1.09 followed by 10 zeros

      That’s a lot of rice pudding.

    • Photo: Eva Bachmair

      Eva Bachmair answered on 14 Jun 2011:

      Ok, I am adding one to that: how heavy would the heaps of rice be? I take one rice grain as 25 mg.

      So Chris’s heap is 2500000 tonnes; imagine 62500 trucks with loading 40 tonnes each on a distance of 1063 km thats about all the lenght of the UK from Nord to South.

      Michael’s heap is smaller with 27250 tonnes; that’s only 681 trucks queueing for 11.5 km.

      Wow!

    • Photo: Philip Denniff

      Philip Denniff answered on 14 Jun 2011:

      What is there left for me say, you have done all the maths.
      The story goes that the inventor of the game of chess was paid in rice. One grain on the first square, two on the second, four on the third, eight on the fourth and so on doubling each time (a power series). Not much of a payment you might think but he died a wealth man, with enough rice for Chris to make her daisy chain and half of Michaels.

    • Photo: Paddy Brock

      Paddy Brock answered on 14 Jun 2011:

      It could depend on your perspective too. Biologists have to be very careful with this as many nautral systems are inconnected. For example, right now I can make a loop around the sun with 14 rice grains by sticking them onto the surface of the kitchen window in a circle. (However, I’m also using this as a cheeky way to get out of using maths!)

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