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Please help! desprate!

  1. Feb 28, 2005 #1
    I have a problem with an acceleration lab im trying to write up.

    i came up with the following values for my points.

    time (seconds) = 0, 0.05, 0.15, 0.25, 0.35, 0.45, 0.55, 0.65, 0.75, 0.85, 0.95
    average velocity (cm/s) = 0, 36, 78, 108, 143, 138, 249, 235, 278, 301, 334

    when plotting the line of best fit for the graph (as suggested by my teacher) i found the line did not cross at (0,0). this was mentioned in my class as something that should happen. what is the source of error that would cause this line to cross the y-axis above the origin, if the starting values were both zero? noone in my class knows

  2. jcsd
  3. Feb 28, 2005 #2
    It depends on what exactly you were doing in lab, but here's the general rule of thumb: nothing will ever be perfect in the physcs lab. Did you have a slow reaction time when recording the time? Was there friction or air resistance? Of course there was, and you never accounted for these factors yet they contributed to your data. As a result they are going to show up on your graph.
    Step away from the graph and look at your y intercept. Are they positive or negative in value? More importantly, what does that actually mean if your intercept is positive or negative based on what you were graphing in the first place?
    Hope this helps and gives you a nudge in the right direction. :smile:
  4. Mar 1, 2005 #3
    Just for thought....when you were plotting the graph, did you put in (0,0) as one of your coordinates? Because I've had a few labs that have done the same thing and when I put in the origin as one of the coordinates, the problem corrected itself.

    I don't know if that helps ya, but just food for thought. :smile:
  5. Mar 1, 2005 #4


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    When plotting the best fit line, were you doing it by hand or were using a program like Excel?
  6. Mar 1, 2005 #5
    It is the gradient that matters after all, so take it although the best fit line doesn't pass through the origin. If the (0,0) is indeed far from the line, then there must be serious errors with the measurments.
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