Author Topic: what is the elegant way to make EJS measure a true period of an oscillation?  (Read 8014 times)

lookang

  • Hero Member
  • *****
  • Posts: 1774
  • http://weelookang.blogspot.com
    • lookang web
what is the elegant way to make EJS measure a true period of an oscillation?

I want to make a pendulum to measure the true period.

i tried

if ( omega < 0.001 & omega > -0.001 ) {  // my inital idea how to detect the end points of the oscillation
  count = count+1;  // make count increase by 1 if condition met
}


if (  count ==2 ) {  // count =2
  T1 = t ;  // T1 = t
}

it doesn't work.

any tips work to do it?

Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
1. The AND operator operator you want is && not &.
 & is bitwise AND

2.
if ( omega < 0.001 && omega > -0.001 ) 
is not a good condition
What if acceleration is very small, omega still smaller then 0.001 in two or more time step.
And if the pendulum starts with omega=0, you might get half period only.

What about define a omegas to store previous omega and change the condition to

if( omega*omegas<0){
 count=count+1;
}
omegas=omega;/save old value
if(count==2){
 T=t-ts;// period=time differences, not necessary starts from t=0
 ts=t;
 count=0;//you need to reset the counter, unless you only want to calculate the first period
}
However, the above code work only if the pendulum starts with omega=0;

lookang

  • Hero Member
  • *****
  • Posts: 1774
  • http://weelookang.blogspot.com
    • lookang web
indeed an elegant/clever way to find true period.

thanks!

will try to implement into my pendulum asap

if( omega*omegas<0){
 count=count+1;
}
omegas=omega;//save old value
if(count==2){
 T=t-ts;// period=time differences, not necessary starts from t=0
 ts=t;
 count=0;//you need to reset the counter, unless you only want to calculate the first period
}

will update my progress on your forum soon :)
« Last Edit: January 14, 2009, 04:41:47 pm by lookang »