Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Solving for Stiffness using a plot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99974] Re: Solving for Stiffness using a plot
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Wed, 20 May 2009 05:03:16 -0400 (EDT)
  • References: <guu2cm$65p$1@smc.vnet.net>

I'm not sure what you mean by saying that you solve for k, but I know
that NDSolve does not want symbolic parameters. You have to assign a
value to k.

You also have to change the square brackets in k[x1[t] - x2[t]] to
round ones: k(x1[t] - x2[t]).

Additionally, you probably forgot a minus sign. And acceleration seems
to depend on positions squared. For springs the relationship usually
is m a = -k x.

The following works:

m1 = 220;
m2 = 300;
v0 = 12;
k = 1000;(*temp.I am solving for this*)
a =
 NDSolve[{-k (x1[t] - x2[t]) - m1*x1''[t] == 0,
   m1*x1''[t] - m2*x2''[t] == 0, x1[0] == 0, x2[0] == 0, x1'[0]=
 == v0,
    x2'[0] == 0}, {x1[t], x2[t]}, {t, -10, 20}]
dis = Plot[Evaluate[{x1[t] - x2[t]} /. a], {t, -10, 20}]

Cheers -- Sjoerd

On May 19, 12:41 pm, twoseat <caseyktimm... at gmail.com> wrote:
> Hello
>
>  I am trying to use mathematica to solve for the stiffness of a spring =
system but I cannot figure out how to plot my equations correctly.
>
>  I have:
> m1=220;
> m2=300;
> v0=12;
> k; (*temp. I am solving for this*)
>
> a = NDSolve[{k[x1[t] - x2[t]]*(x1[t] - x2[t]) - m1*x1''[t] == 0,
>    m1*x1''[t] - m2*x2''[t] == 0,  x1[0] == 0,  x2[0] ==
= 0,  
>    x1'[0] == v0, x2'[0] == 0}, {x1[t], x2[t]}, {t, -10, 20}]
> dis = Plot[Evaluate[{x1[t] - x2[t]} /. a], {t, -10, 20}]
>
> This gives me multiple errors and wont plot.
>
>  I am going to try to plot k[x1[t]-x2[t]]*(x1[t]-x2[t]) vs (x1[t]-x2[t]=
) to solve for k but I can't determine how to set up my equations to plot.
>
> Any help or recommendations would be appreciated!



  • Prev by Date: Re: Filenames with ToString
  • Next by Date: Re: Could some one please help
  • Previous by thread: Re: Solving for Stiffness using a plot
  • Next by thread: Are you wolfing tonight?