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

Earth and Ladders

  1. Mar 16, 2006 #1

    Pyrrhus

    User Avatar
    Homework Helper

    If you put a ladder throught the Earth going throught its center, and if you go down it with your head pointing to the Earth's surface and feet to the centroid, passing throught Earth's centroid and heading to the other surface, you will go out with your head pointing to the surface and feet to the Earth's centroid. Why?
     
  2. jcsd
  3. Mar 16, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Because unless you are comfortable climbing a ladder upside down (with respect to the gravitation field) you will be motivated to turn around. :wink:
     
  4. Mar 17, 2006 #3
    Lets discuss what is hapenning at the centroid. Coz that is where the question really matters? Please dor eply.
     
  5. Mar 17, 2006 #4

    Doc Al

    User Avatar

    Staff: Mentor

    The gravitational field at any radius always points towards the center of the earth. The effective acceleration due to gravity varies (linearly) from 0 at the center to the usual value of g at the earth's surface.
     
  6. Mar 17, 2006 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Well, it say "heading to the surface" so obviously you turn your head to the surface when you pass the center of the earth!
     
  7. Mar 17, 2006 #6

    Doc Al

    User Avatar

    Staff: Mentor

    :rofl: I think you've cracked this riddle!
     
  8. Mar 19, 2006 #7

    Pyrrhus

    User Avatar
    Homework Helper

    hahahah, Thanks for the replies. I was just wondering if it was something special or whatever.
     
  9. Mar 23, 2006 #8
    wouldn't the gravitational pull increase as you neared the center of the earth? according to the law of universal gravitation, wouldn't r approach 0 and thus when you are at the center the gravitational force would be infinite?
     
  10. Mar 23, 2006 #9

    Doc Al

    User Avatar

    Staff: Mentor

    No. The gravitational field at the center is zero.

    The gravitational pull at a distance r from the earth's center is only due to the mass contained within the sphere of radius r. (The outer shell contribution cancels.) While the the gravitational pull does increase according to M/r^2, M is proportional to r^3: the net effect is that the effective field strength is proportional to r. It's zero at the center (where r = 0) and the usual g at the surface.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Earth and Ladders
  1. Ladder Circuit Paradox (Replies: 3)

  2. It is earthed or not? (Replies: 6)

  3. Rotation of earth (Replies: 4)

  4. Balloon on Earth (Replies: 7)

Loading...