Can someone tell me why NDsolve isn't working here?

• To: mathgroup at smc.vnet.net
• Subject: [mg44022] Can someone tell me why NDsolve isn't working here?
• From: mizrandir at hotmail.com (Mizrandir)
• Date: Sat, 18 Oct 2003 03:12:14 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Hello, Im trying to solve a system of 6 differential equations with
NDSolve but I can't get Mathematica to do it. I wrote:

R = 1;
M = 1;
L = 1;
NDSolve[{Rx[t] + Fx[t] == 2M x''[t], Ry[t] + Fy[t] == 0,
Fx[t] R == -M R x''[t], -Rx[t] ==
M x''[t] + (M L \[Theta]''[t] Cos[-\[Theta][t]])/
2 + (M L \[Theta]'[t]^2 Sin[-\[Theta][t]])/2, -Ry[
t] == (M L \[Theta]''[t] Sin[-\[Theta][t]])/
2 - (M L \[Theta]'[t]^2 Cos[-\[Theta][t]])/
2, -(L Cos[\[Theta][t]] Rx[t])/2 + (L Sin[\[Theta][t]])/
2 == (M L^2 \[Theta]''[t])/12, x[0] == 0, \[Theta][0] ==
Pi/2,
Ry[0] == -M/2, Rx[0] == 0, Fy[0] == 5M/2, Fx[0] == 0}, {x,
\[Theta], Ry,
Rx, Fy, Fx}, {t, 0, 1}]

And Mathematica gave me the following error:

NDSolve::"ndode": "Input is not an ordinary differential equation."

Does anybody know what am I doing wrong. Can I use Mathematica to
solve this?