1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Check on Tangents.

  1. Sep 12, 2005 #1
    Just making sure that the proper forumla to calculate a tangent on a graph, (Position vs. Time) that shows an accelerated motion is rise/run.

    And also, I would like to make sure that if it asks you to start at the point 0.15s, that as long as you draw the line to cross a point without going through the line, you can virtually pick any point on the x and y axis to produce the correct answer, as long as the line touches the starting point on the x axis.

    Thanks for reading, and any response is greatly appreciated.
  2. jcsd
  3. Sep 12, 2005 #2


    User Avatar
    Science Advisor

    This not at all clear. You talk about "graphs" but you seem to be thinking specifically about motion. If you have a "distance versus time" graph, with constant acceleration, then the graph is NOT a straight line, the slope of the tangent line at any point varies with the point, and the slope is not "rise over run" since neither is those is defined at a single point. The slope of the tangent line can be calculated by taking the derivative.

    It is true that for a straight line, you can use whatever (x,y) points you want (on the line of course) to calculate the slope- that's true since the slope of a straight line IS a single number and is independent of the points you use to calculate (y1- y0)/(x1-x0). SO if you (accurately) draw the tangent line (that may be what you meant by "draw the line to cross a point without going through the line") then you can use any two points on that tangent line to find the slope of the tangent line.

    (Though I might point out that the "tangent line" to y= x3 at x= 0 does "go through" the graph!)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook