Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Floating Rock Raft

  1. Aug 11, 2012 #1
    Can anyone answer a couple of questions about the new floating rock raft off New Zealand ?

    How much mass does it contain ?

    Where is it headed ? ( or will it disperse ? )
     
  2. jcsd
  3. Aug 11, 2012 #2

    Evo

    User Avatar

    Staff: Mentor

    Please post a link, do not make members hunt for the source.
     
  4. Aug 11, 2012 #3

    Bobbywhy

    User Avatar
    Gold Member

    It has just been discovered around 09 August and there have been not published estimates of its total mass, as far as I know.

    http://www.bbc.co.uk/news/science-environment-19207810
    http://news.yahoo.com/bizarre-rock-ice-shelf-found-pacific-104349304.html [Broken]

    .
     
    Last edited by a moderator: May 6, 2017
  5. Aug 11, 2012 #4
    Last edited: Aug 11, 2012
  6. Aug 12, 2012 #5

    davenn

    User Avatar
    Science Advisor
    Gold Member

    well time for you to try some maths ;)
    you have some of the info, and wiki will provide the rest

    its 26,000 sqr km x ~ 600mm (0.6metre thick)

    wiki gives an example of ~ 0.25 g / cubic cm for pumice

    work out the volume from the first 2 measurements then multiply it by the density

    watch your values I would suggest get everything into cubic metres rather than trying to work with km, cm etc


    Dave
     
  7. Aug 12, 2012 #6
    Last edited: Aug 12, 2012
  8. Aug 13, 2012 #7

    davenn

    User Avatar
    Science Advisor
    Gold Member

    yup some bad maths there I think ;)

    26,000 sqr km = 26,000,000 sqr metres ( 26 million) x 0.6 metres = 15,600,000 (15.6 million) cubic metres

    0.25g / 1ccm => 2.5g / 10 ccm => 25g / 100ccm (ccm = cubic cm) 100ccm = 1 cubic metre

    25g = 0.025kg

    15,600,000 cubic metres x 0.025kg = 390,000 kg = 390 tonnes ( 1 Tonne = 1000kg)

    some one check my maths please :)

    Dave
     
  9. Aug 13, 2012 #8
    Those numbers aren't right. I reckon:

    26,000 sqr km = 26,000,000,000 sqr metres

    0.25g / 1ccm = 250 kg/m3

    EDIT: Imagine a cubic metre of rock. Now how much does that weigh? 25 grams? No way!
     
  10. Aug 13, 2012 #9

    davenn

    User Avatar
    Science Advisor
    Gold Member


    crap, I really screwed up my calcs.. doh.... I'll bow to your better maths, no wonder I failed school cert maths twice haha

    after using some online convertors I agree with your m2
    I will work on the rest as well

    Dave
     
    Last edited: Aug 13, 2012
  11. Aug 13, 2012 #10

    davenn

    User Avatar
    Science Advisor
    Gold Member

    using online calculators

    gosh am getting such huge numbers its freaky haha
    I need to work through this for my own understanding/sanity please correct me if I go wrong

    so 10,000 cm2 = 1 metre2

    therefore 10,000 x 10,000 x 10,000 cm = 1 m3

    now here's something that has always caught me out....
    thats 1 with 12 0's is that the same as 1 x 1012 or 1 x 1011 .... I was thinking 11

    Dave
     
  12. Aug 13, 2012 #11
    Hi Dave

    1 m = 100 cm
    1 m2 = m * m = 100 cm * 100 cm = 10,000 cm2

    You got that bit right.


    Next:

    1 m3 = m * m * m = 100 cm * 100 cm * 100 cm = 1,000,000 cm3

    You slipped up with that bit.

    Incidentally: 1 with 12 0's is the same as 1012.

    This stuff is not really maths. It's just working with units. Try to picture a square metre, then imagine how many square cm would fit inside it, then try to imagine a cubic metre and image how many cubic cm would fit inside it. The maths just drops out of the mental picture.

    Cheers
     
  13. Aug 13, 2012 #12

    davenn

    User Avatar
    Science Advisor
    Gold Member

    OK thanks

    yeah something that will trip me up easily haha
    i will continue working through this in this thread cuz I eventually want to confirm for myself the cubic volume and mass of the pumice .... besides there may be others that learn something too haha

    OK so we have 26,000,000,000 metres2 and for an avg lets just pick 0.5 m thick = 13,000,000,000 m3

    now the fun of converting 0.25g / cm3 to kg / m3

    0.25 x 1,000,0003 (1m3) = 250,000g / 1m3 = 250kg / 1m3
    which is what you said earlier, billiards :)

    so 13,000,000,000 m3 x 250kg / 1m3 = 3,250,000,000,000 kg = 3,250,000,000 metric Tonnes

    OK how did I go that time ? :)

    Dave
     
  14. Aug 14, 2012 #13
    good that time :) - I use a depth 0.6 to get the 3.9 billion verse 0.5 to get 3.2
     
    Last edited: Aug 14, 2012
  15. Aug 14, 2012 #14
    Good but the thickness assumption is probably whacky.


    One article says the pumice fragments are golf ball sized.

    Now golf balls have a diameter of about 5 cm. So I would scale down your answer by a factor of 10 (dave).

    Then there is the issue that this thickness is not uniform over the areal extent. You could make another assumption -- e.g. close hexagonal packing -- to account for the gaps in between the pumice fragments: multiply your answer again by 0.74.
     
  16. Aug 14, 2012 #15

    davenn

    User Avatar
    Science Advisor
    Gold Member

    yes agreed, the calcs were for a uniform thickness/density, but at least I finally got my units and maths sorted out haha

    D
     
  17. Aug 15, 2012 #16
    Awesome. Glad to be able to help out
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Floating Rock Raft
  1. Name these rocks (Replies: 9)

  2. Layered rock. (Replies: 5)

  3. A rock that rattles? (Replies: 4)

  4. What's that rock (Replies: 8)

Loading...