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Position ~ Time Graph vs Displacement ~ Time Graph

  1. Sep 16, 2012 #1
    1. Are these two the same? I'm not sure. Sometimes my teacher labels the Y axis with a Delta Displacement [E]. Other times it's just Position (M), so I'm not sure how to identify if we are finding Speed or Velocity.

    I'm just assuming they are the same.

    2. Also, position is a Vector quantity, but if it's not given a direction, can we assume it's the same as distance?

    Last edited: Sep 16, 2012
  2. jcsd
  3. Sep 16, 2012 #2

    Simon Bridge

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    Welcome to PF;
    1. They are not the same, and the one you want should be clear from the context.

    displacements have a direction ... if you all the way around a circle with radius R, back to where you started, then you have traveled a distance ##d=2\pi R## but your displacement is ##\vec{d}=0##.

    2. No. again, the directions should be clear from the context ... if not, define some that make sense to you. Often motion is in 1D or along a track so you can only go forward or backward, then one direction is just shown as positive and the other one as negative.

    Care must be taken over the signs of acceleration vectors in that case since a negative acceleration could mean you are slowing down in a + direction or speeding up in the - direction.
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