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

Balls puzzle.

  1. Aug 10, 2008 #1
    You have 2 balls. Both are identical in size and mass, but one is made of gold and is hollow,the other is not hollow and made from titanium. Find out which is which ball, and lets say both are covered with a black paint that is anti reflective, heat/electricity insulator. You can't use any measurement device, nor hitting, damaging or breaking the ball..

    P.S: There's a really simple way.
  2. jcsd
  3. Aug 10, 2008 #2


    User Avatar
    Gold Member

    Knock them? One will sound hollow?
  4. Aug 10, 2008 #3
    Mmm.. lets say the paint is anti-acoustics.
  5. Aug 10, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Roll the balls side-by-side down a ramp. The solid ball will roll faster.
  6. Aug 10, 2008 #5
    wheew.. you're fast..
  7. Aug 10, 2008 #6


    User Avatar
    Gold Member

    Around here, we like our women that way. :devil:
  8. Aug 11, 2008 #7
    drop them in water. the hollow one will bob higher.

    oh..same mass, never mind
  9. Aug 11, 2008 #8
    Nice try.
  10. Aug 11, 2008 #9


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Remove the paint?
    (This as an alternative to lisab's suggestion)
  11. Aug 11, 2008 #10
    oohh rigid bodies thats realy good
  12. Aug 11, 2008 #11
    put them in a bucket of water
    they vary in density
    the gold will pull out more water
    am i correct?
  13. Aug 11, 2008 #12
    As I said, you can't damage nor break the ball, and removing the paint would be considered damaging. But yeah, lisab's answer is right.
    Both would pull same amount of water because both are same size and mass, so they have same volume and density.
  14. Aug 11, 2008 #13


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    I think black is a damaging colour, I'm merely prettifying the balls..
  15. Aug 11, 2008 #14
    aaahhh disregard it
    you sayed that the gold ball is hollow
  16. Aug 11, 2008 #15
    No, imagine a gold sphere as an "o" the black line is gold and the white is hollow... The titanium sphere is all solid.
  17. Aug 11, 2008 #16
    if you shoot them out of a cannon
    the gold ball will not fly in a steady trajectory
    because its hollow

    in order to fly in a steady way you need to have a full ball

    because from my knowledge
    the AK bullets have a shifted center of mass
    which make them highly unstable
    and when they hit a person
    instead of going forward
    they are starting to swirl inside the victim

    am i correct?
  18. Aug 11, 2008 #17


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    The middle of the gold ball is empty, some one, it is hollow.

    The hollowed gold ball can perfectly well have the same size and mass as the compact titanium ball
  19. Aug 11, 2008 #18
    Actually I don't know. I didn't went that far.
  20. Aug 11, 2008 #19


    User Avatar
    Homework Helper

    Titanium is paramagnetic.
  21. Aug 11, 2008 #20
    i am not a physicist but i had some small experience with fire arms

    and i know for a fact that bullets with a shifted center of mass
    are swirling inside the victim instead of going threw him

    the question is whether the hollow ball considered to have a shifted center of mass
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Balls puzzle.
  1. A Chessboard Puzzle (Replies: 1)

  2. A Dinner Puzzle (Replies: 11)

  3. Trigonometry puzzle (Replies: 5)

  4. Puzzle for you (Replies: 1)

  5. Ippossible puzzle? (Replies: 12)