1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: A kind of Fermi Questions

  1. Dec 2, 2012 #1
    1. How many sands on the earth?

    2. Hints: Using the Fermi estimation

  2. jcsd
  3. Dec 2, 2012 #2


    User Avatar
    2017 Award

    Staff: Mentor

    What did you do so far? Where did you run into problems?
    What is "sands"? Do you mean grains of sand?
  4. Dec 2, 2012 #3
    Yes, I mean the "grains of sand"

    I do not really understand your first two questions.
  5. Dec 2, 2012 #4


    User Avatar
    2017 Award

    Staff: Mentor

    From the board rules:
    This is not a board where others do your homework. We can help you if you run into problems, but it is your homework.
  6. Dec 2, 2012 #5
    Oh,yes. When I first saw this question, I have no idea about that. However, now I know that this question is a kind of Fermi questions, which need appropriate estimation.

    But the problem is that I do not know how to start. There is another Fermi question, " How many Piano Tuners in New York? " , I can do that by using the estimation of the population of NY, the amount of pianos, the working time of Tuners, etc.

    However, when I am asked for "How many grains of sand? ", I don't know what data should I use to estimate
  7. Dec 2, 2012 #6


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    One way to approach it is to think about what parameters, if changed, would radically change your answer. E.g. if all the sand grains were a million times smaller than they actually are, that would make a lot more of them. Would this alter any other information available to you? If not, having an estimate for average grain size will be essential.
  8. Dec 2, 2012 #7
    I found this short book on order of magnitude estimation rather helpful

  9. Dec 2, 2012 #8
    Thank you very much, thats very helpful
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook