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Lc physicsNewtons second law F=ma graph

  • 24-10-2005 09:13PM
    #1
    ublinia2
    Closed Accounts Posts: 114 ✭✭


    For the Netowns second law graph F=ma and you are graphing F against a ,
    which goes on which axis?

    I always thought that it was F on the y axis , and a on the x axis as when you get the slope it should equal m.

    i.e F/a =M

    but I have checked two books , Rapid revision Physics and another one and the both say that a is on the y axis and F on the x axis

    The only reason for this is traditionally the thing you vary is normally on the
    x axis ( which is F in this experiment)

    Which method is correct by the department ?


Comments

  • #2
    Delphi91
    Registered Users, Registered Users 2 Posts: 1,501 ✭✭✭Delphi91


    ublinia2 wrote:
    For the Netowns second law graph F=ma and you are graphing F against a ,
    which goes on which axis??

    The way I've always taught graphs is that the independent variable goes on the x-axis. In other words, the value that you have control over in the experiment.

    For Newtons 2nd Law, if you're using a trolley with masses attached to it over a pulley causing it to accelerate, then the force is the independent quantity - the acceleration of the trolley is therefore dependent on the force.

    So I would plot F on the x-axis and a on the y-axis.

    Following the idea that a straight line graph can be represented by the eqn y = mx + c, you get

    a = f/m

    or

    a = (1/m)f

    In other words, the graph has a slope of 1/m where m is the mass of the trolley.

    Mike


  • #3
    dudara
    Registered Users, Registered Users 2 Posts: 33,518 ✭✭✭✭dudara


    Yup, that's the correct thinking. The variable that you're in control of, namely F, goes on the x-axis. The dependant variable, or the one that you're measuring, a, goes on the y-aixs.

    Follow this rule, and you can't go wrong. The standard way of writing Newton's Second Law, F = ma, just makes it seem the other way around. Think of it in terms of independant and dependant variables and you'll be fine.


  • #4
    ublinia2
    Closed Accounts Posts: 114 ✭✭ublinia2


    Does it make any difference if I plot F ( y axis)against a (x axis) for the Leaving cert as the slope of the graph will then give me m directly ie
    f/a = m

    Or do i have to plot them with the thing I vary on the x axis regardless (of what way the slope will turn out.)

    Will i lose marks for choosing one thing over another ?


  • #5
    Delphi91
    Registered Users, Registered Users 2 Posts: 1,501 ✭✭✭Delphi91


    Well, I would always draw a graph with the independent variable on the x-axis and the dependent variable on the y-axis. You do it with coordinate geometry when you plot quadratic/cubic equations (think about it!!)

    You won't lose marks for doing it the other way - the marking schemes don't indicate a preference.


    Mike


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