use of matlab in physics

Question

Tor Fredrik Hove 2012-2-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/27943-use-of-matlab-in-physics

采纳的回答： the cyclist

在 MATLAB Online 中打开

You have a force from many forces that is

F=F+Fc-Fv-D

where

F=400 N
Fc=488*exp(-(t/0.67)^2)  N
Fv=25.8v
D=0.34911(1-0.25*exp(-(t/0.67)^2)*v^2

i was asked to use eulers method to calculate in matlab the position of a runner who is moving with these forces (F is moving forward motion, Fc is extra motion forward when body is leaned and back is curled, Fv is a force that prevents F to continue to infinity and decreases acceleration as function of v of runner and D is airdrag)

here is what i wrote but without clearly getting a right answer:

vl=[];
x=[];
t=[];
a=[];
vl(1)=0;
n=2;
x(1)=0;
t(1)=0;
dt=0.05;
while x(n-1)<100
      F=5;
      Fc=6.1*exp(-(t(n-1)/0.67)^2);
      Fv=25.8*vl(n-1);
      D=0.34911*(1-0.25*exp(-(t(n-1)/0.67)^2))*(vl(n-1))^2;
      a(n-1)=F+Fc-Fv-D
vl(n)=vl(n-1)+a(n-1)*dt;
x(n)=x(n-1)+vl(n)*dt;
t(n)=t(n-1)+dt;
n=n+1;
end
   plot(t,vl,'r');
hold on
plot(t,x,'g');
legend('vl','x');

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Answer 1

the cyclist 2012-2-3

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/27943-use-of-matlab-in-physics#answer_36200

I notice two things:

You run your while loop out to x=100 or so, but with the constants you have, all the interesting action is taking place at x<1. Temporarily, you might consider changing the limit to x(n-1)<1, while you debug.
You divided two of your force constants (F and Fc) by a factor of 80, but you did not do the same with the other two (Fv and D). I did not look in detail (something with units, which you did not specify?), but that might lead to the current incorrect behavior, where the runner reaches top velocity in about a second.

I suggest you write out your equations with the units included, to ensure that the units all match.

There are also some significant MATLAB-specific improvements that could be made to your code, but I think you should focus on getting the physics/math correct first.