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Fnet vs a GRAPH?

  1. Oct 11, 2008 #1
    Fnet vs a GRAPH???

    Im trying to understand how to do a Fnet vs a graphic. I have a Xposition vs time, Yposition vs time, Xvelocity vs time and a Yvelocity vs time. They want me to make a Fnet vs a graph with this but i have no idea how to do it. Someone can help me please?
    Thank you
  2. jcsd
  3. Oct 11, 2008 #2


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    Re: Fnet vs a GRAPH???

    Force(net) = mass * acceleration

    If you have a velocity function and find the derivative of it (slope of the velocity vs. time graph), you get acceleration.

    Am I answering your question? Perhaps you may want to provide a bit more background.
    Last edited: Oct 11, 2008
  4. Oct 11, 2008 #3
    Re: Fnet vs a GRAPH???

    rate (s)= 0,05 atheort (cm/s^2)= 91,3559322

    t X Ycm tmidpt Vx Vy
    cm/s cm s cm/s cm/s Vox (cm/s) 36,19
    0,0 0,0 0,0 xxx xxx xxx Voy (cm/s) 31,60
    0,1 3,8 2,7 0,1 38,0 27,0 Vo (cm/s) 48,04
    0,2 7,4 4,4 0,2 36,0 17,0
    0,3 11,1 5,1 0,3 37,0 7,0 qo (rad)= 0,72
    0,4 14,1 4,8 0,4 30,0 -3,0 qo (deg)= 41,13
    0,5 18,3 3,6 0,5 42,0 -12,0
    0,6 21,8 1,4 0,6 35,0 -22,0 Ymax 5,11
    0,7 25,4 -1,8 0,7 36,0 -32,0 Range 23,41
    0,8 28,7 -6,0 0,8 33,0 -42,0
    0,9 32,6 -11,1 0,9 39,0 -51,0 Ymaxtheo (cm) 5,11
    Ymaxexp (cm) 5,10
    % deviation Ymax -0,20
    Vox (cm/s) 36,19
    ay (cm/s^2) -97,66 Rangetheo (cm) 23,60
    Voy (cm/s) 31,60 Rangeexp (cm) 23,41
    % deviation range -0,81

    These are my data. I did 4 graphs with them (listed above) Actually the lab's objective is to examine the motion of a projectile simulated on a inclined air table (with spark rate fixed at 50miliseconds) Then we can observed a bunch of points (making a reversed 2nd degree function) and take the X values on time, Y values etc...
    I know im not 100% clean , sorry but you help is really apreciated. So with this said...im looking for a Fnet versus a graph
  5. Oct 11, 2008 #4


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    Re: Fnet vs a GRAPH???

    Welcome to PF.

    What is the basic definition of acceleration?
  6. Oct 11, 2008 #5


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    Re: Fnet vs a GRAPH???

    Acceleration is a change in velocity. That can happen in two ways (since velocity is a vector):

    1. The magnitude can change, indicating a change in speed.
    2. The direction can change, indicating a change in direction.

    So, if a vehicle is driving down a road and makes a right, but the speed of the vehicle remains the same, the vehicle is still accelerating because the velocity changes (2.). An increase or decrease in speed is called acceleration, as well. In everyday life, people use the word deceleration to indicate a decrease in speed. In physics, *any* change in magnitude (speed) or direction is considered an acceleration. So, if you speed up, slow down, or change direction, you are accelerating.

    Acceleration can be found visually by finding the slope of the velocity vs. time graph of an object.

    Math-wise, acceleration is the derivative (slope, rise-over-run) of the velocity function. If you have a V vs. T graph of an object, you can find the acceleration of the object at any time by evaluating the slope of the graph at that instant.
  7. Oct 11, 2008 #6


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    Re: Fnet vs a GRAPH???

    If you're doing this graph in Excel using the chart wizard, create a velocity vs. time graph. From the velocity vs. time graph, you need to find the slope (rise over run [change in y over change in x]) at each point you have plotted. For each value that you have just found the slope for, create a separate graph that graphs those. That's your acceleration vs. time graph.

    Now, using F=ma (force equals mass times acceleration), you know that acceleration equals force over mass. Just plot points in Excel that are acceleration times mass to get a F vs. T graph.
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