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Help me out here

  1. Mar 23, 2008 #1
    help me out here plz

    what exactly is this equation :


    and what is g
  2. jcsd
  3. Mar 23, 2008 #2
    It's a kinematics equation relating the final and initial displacements, the initial velocity, time, and the acceleration of gravity, g.
  4. Mar 23, 2008 #3


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    Welcome to PF!

    Hi hamudi! Welcome to PF! :smile:

    It's [tex]x(t)\,=\,\frac{1}{2}gt^2\,+\,v_0t\,+\,x_0\,,[/tex]

    and it's the constant-acceleration equation for the distance x reached after time t with constant acceleration g if you started (at time 0) at position x0 and with speed v0. :smile:

    "g" usually means "gravity", by the way - if it was anything else, you'd probably use the letter "a" (for "acceleration", of course).
  5. Mar 23, 2008 #4
    Yes, Tiny-tim is correct; a (acceleration) in your equation is g because it is probably looking to y axis and of course acceleration in y axis is downward g

    when ever you get confused what is a parameter you can look to its dimension too, in here g has acceleration dimension. [L/(T^2)]
  6. Mar 23, 2008 #5
    hey thanks ...that was a great help =)
  7. Mar 24, 2008 #6
    wat exactly is the purpose of the equation
  8. Mar 24, 2008 #7
    For physics problems relating those variables.
  9. Mar 24, 2008 #8
    can the constant g change ..... like for example in one testing of an object it is 9 and on the other object( a diffrent one) 10.6 ....is this possible
  10. Mar 24, 2008 #9
    no g is always equal to -9.8 m/s^2. though the sign changes according to the orientation of the coordinate system
  11. Mar 25, 2008 #10
    It depends only on location. We have this value of g near the surface of the earth. Slightly different values in cities of different altitudes -- in Poughkeepsie, New York it happens to be 9.80665 -- but who cares about the way-out decimal places? It changes slightly while falling through different altitudes, if it's a very long drop. Very different values on other planets -- on Mars it's about 3.2 m/s^2.
  12. Mar 25, 2008 #11


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    Hi hamudi! :smile:

    As mikelepore says, it changes in different locations.

    But in the same place, it does stay the same. :smile:

    (If it didn't, we wouldn't use the letter "g".)
  13. Mar 25, 2008 #12
    thx...well yeah that does make sense :rofl:
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