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Graph motion

  1. Nov 24, 2011 #1
    in acceleration time graph when the acceleration is constant. Then at an instant it has negative acceleration. Does this mean that the body is decelerating or it is accelerating in the opposite direction. eg. http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/motgraph.html {last graph}
     
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  3. Nov 24, 2011 #2
    When an object decelerates it usually means that the acceleration vector points in the opposite direction of the velocity vector. So when you apply a negative acceleration to an object it decelerates until its velocity reaches zero then it begins to accelerate in the direction opposite of the original motion.
     
  4. Nov 24, 2011 #3
    how can u tell from the graph when the object comes to rest?
     
  5. Nov 24, 2011 #4

    Redbelly98

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    Phrases such as "comes to rest", "is at rest", and "starts from rest", all refer to the velocity. The answer lies in the velocity graph, because being at rest means that the velocity is equal to _____?
     
  6. Nov 24, 2011 #5
    i was referring to the acceleration time graph.
     
  7. Nov 24, 2011 #6

    Redbelly98

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    It cannot be determined from the acceleration graph alone. You would need to know the velocity at some point in time, then it could be determined by taking the integral of the acceleration. (Have you taken a calculus course that covers integrals?)
     
  8. Nov 24, 2011 #7
    my only problem is with the acceleration time graph. lets say a body is moving with constant velocity. THen in an instant it stops and accelerates in the opposite direction. Then wouldnt the graph be same as the graph mentioned above?
     
  9. Nov 25, 2011 #8

    Redbelly98

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    No, the acceleration graph would be different:
    Okay. What is the acceleration while the body is moving with constant velocity?
    If it stops "in an instant", the acceleration would be -∞ for that instant. In actually, the body would stop in a very short time (not an really an instant), and the acceleration would have a very large magnitude and be negative.

    Hope that helps.
     
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