1. Not finding help here? Sign up for a free 30min 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!

Newton measures the speed of gravity

  1. Feb 26, 2012 #1
    1. The problem statement, all variables and given/known data

    This doesn't come from a textbook but it's like a homework question so I thought it would be more appropriate here.

    Screenshot2012-02-26at72344PM.png

    Screenshot2012-02-26at72340PM.png



    I'm trying to figure out what equation Newton used since the force of gravity or the mass of the Earth was not known until Cavendish. I'm looking for an equation that has the square of the distance or the radius, but all I can find is

    (Gm1m2)/r^2 = (m2v2)/r

    But Newton couldn't have used that one because he didn't know G or the mass of the Earth. I also thought about a = (v^2)/r but Newton didn't know the acceleration.
     
    Last edited: Feb 26, 2012
  2. jcsd
  3. Feb 26, 2012 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    In this case, you can calculate the acceleration of the moon from its angular speed and radius:

    a = v^2/r = 4∏^2r/T^2

    By measuring the acceleration of the moon and of an object on the surface of the earth, you get the 1/r^2 relationship.

    AM
     
    Last edited: Feb 26, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Newton measures the speed of gravity
  1. Gravity Measurement (Replies: 1)

  2. Measuring gravity (Replies: 2)

Loading...