relations between displacement/velocity/acceleration

[Fu-Kwun Hwang]

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Drag the blue dots in the V-t diagram to set up how the velocity changes as a function of time.
Press play to watch how the x-t and a-t diagrams changed with the setting.

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[lookang]

i am trying to make the text to appear which i have not problem with now..


the simple text like


else if (a>-0.1&&a<0.1 ) // v constant

{
title="Speed is uniform(constant)! |v| = "+dvalue(speed)+" m/s ";

}

is very simple to understand and check in java.....


But i have a question,

how to construct the else if checking condition for


1. speed is increasing at constant rate

// is it like this?

else if (  a > 0 && vti > vt ) // how to make java statement to check acceleration is the same as t change?



2. speed is increasing at increasing rate

[lookang]

no worries,
 i think the position of the codes can solve this problem

when t = t + dt,

speed = 10 + 0.1 let say
run the loop to check
assign speedi = speed inside the loop // forcing speedi = 10 let say.

i seems to have solved it from help from people who know more java than me

[Fu-Kwun Hwang]

1. how to check if speed is increasing at constant rate ( or acceleration is a constant)

 if( Math.abs(a)!=0 ){ // constant rate could be negative

}

2.  how to make java statement to check acceleration is the same as t change?

if the acceleration is a, define a new variable a2=a.

At constraint page add the following code

if(_isPlaying()){// make sure we only check this when the simulation is playing,
 if(a==a2){// if a(t) is the same as a2(t-dt)

 }
 a2=a; // make a2 equal a(t)
}

[lookang]

power!!

i will keep in mind

thanks!

[lookang]

any idea how to fix this error message ?

it appears when the applet runs untl the end and stop by itself

java.lang.reflect.InvocationTargetException
   at sun.reflect.GeneratedMethodAccessor21.invoke(Unknown Source)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
   at java.lang.reflect.Method.invoke(Unknown Source)
   at org.colos.ejs.library.control.MethodWithOneParameter.invoke(Unknown Source)
   at org.colos.ejs.library.control.GroupVariable.propagateValue(Unknown Source)
   at org.colos.ejs.library.control.EjsControl.doTheUpdate(Unknown Source)
   at org.colos.ejs.library.control.EjsControl.update(Unknown Source)
   at org.colos.ejs.library.Animation.update(Unknown Source)
   at org.colos.ejs.library.Animation.step(Unknown Source)
   at org.colos.ejs.library.Animation.run(Unknown Source)
   at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 11
   at weexvav05.weexvav05.getV(weexvav05.java:270)
   at weexvav05.weexvav05._method_for_getV_t__variable(weexvav05.java:337)
   ... 11 more
Exception in thread "Thread-2" java.lang.NullPointerException
   at org.colos.ejs.library.control.swing.ControlNumberField.setValue(Unknown Source)
   at org.colos.ejs.library.control.GroupVariable.propagateValue(Unknown Source)
   at org.colos.ejs.library.control.EjsControl.doTheUpdate(Unknown Source)
   at org.colos.ejs.library.control.EjsControl.update(Unknown Source)
   at org.colos.ejs.library.Animation.update(Unknown Source)
   at org.colos.ejs.library.Animation.step(Unknown Source)
   at org.colos.ejs.library.Animation.run(Unknown Source)
   at java.lang.Thread.run(Unknown Source)

[Fu-Kwun Hwang]

If you open weexvav05.java and check for line 270, you will find out the following:

public double getV (double tt) {
  id=(int)(tt/delt);
 if(id < n){
  a=(yv[id+1]-yv[id])/delt; // formula for acceleration
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
 }
 return 0.; // else id = or > n , return getV(tt) = 0
}

if id equal  n-1, then id+1 will be equal to n which is not available
The maximum number of index is n-1

That is why the error is ArrayIndexOutOfBoundsException

You need to fix the above logical error (run time error).

[lookang]

ok i try


this is  work in progress i have made some customized teaching n learning words.

[lookang]

Seems to help solve it  thanks!
by providing  else if id>n to allow a way to return a value. YA!

public double getV (double tt) {
  id=(int)(tt/delt);
 if(id<=n){
  a=(yv[id+1]-yv[id])/delt; // formula for acceleration
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
 }
 
 // hoping to solve error msg at end of sim
 
else if(id>n){
  a=(yv[id]-yv[id-1])/delt; // formula for acceleration change to calculate backward
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
 }
 
  // hoping to solve error msg at end of sim
 
 
 
 return 0.; // else id = or > n , return getV(tt) = 0
}

[Fu-Kwun Hwang]

No! It is not correct.
If the dimension of yv is n, it means that the index for yv is from 0 to n-1;

Code:

if(id<n){
  a=(yv[id+1]-yv[id])/delt; // formula for acceleration
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
}

Run time error will occurs when id equal n-1.
It is even worse if you changed it to id<=n , because error will occur when id equal n-1 or n.
You could change it to

Code:

if(id<n-1){
  a=(yv[id+1]-yv[id])/delt; // formula for acceleration
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
}
  a=(yv[id]-yv[id-1])/delt; // formula for acceleration change to calculate backward
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )

You do not need to add else if(id>=n) , because it will always be satisfied (if it did not satisfied previous if condition).

P.S. I did not check the formula, I only check for logical statement.

[lookang]

cool man

it definitely works now, thanks for the useful codes to copy and paste.

Code:

public double getV (double tt) {
  id=(int)(tt/delt);
 
 
  if(id<n-1){
  a=(yv[id+1]-yv[id])/delt; // formula for acceleration
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
}
  a=(yv[id]-yv[id-1])/delt; // formula for acceleration change to calculate backward
  return yv[id]+(t-T[id])*a; // result for  from a = (getV - yv[id] )/ ( t - T[id] )
 
 
// return 0.; // else id = or > n , return getV(tt) = 0
}

[lookang]

added some teaching needs

Kinematics  Animation to illustrate constant speed, increasing s at increasing/decreasing rates, decreasing s at increasing/decreasing rates, etc. Graphs with animation of object moving at the same time

if (t>=20)
{
title1="";

}


 if (vt==getV(t)&&vt>0) // s increasing constant rate, v constant
{
title1="s ="+dvalue(x)+" m "+"is increasing at constant rate";

}

else if (vt>0&&a>0 ) // s increasing at increasing rate
{
title1="s ="+dvalue(x)+" m "+"is increasing at increasing rate";

}

else if (vt>0&&a<0 ) // s is increasing at decreasing rate
{

title1="s ="+dvalue(x)+" m "+"is increasing at decreasing rate";
}


else if (vt==getV(t)&&vt<0) // s decreasing constant rate, v constant
{
title1="s ="+dvalue(x)+" m "+"is decreasing at constant rate";

}

else if (vt<0&&a<0 ) // s is decreasing at increasing rate
{

title1="s ="+dvalue(x)+" m "+"is decreasing at increasing rate";
}

else if (vt<0&&a>0 ) // s is decreasing at decreasing rate
{

title1="s ="+dvalue(x)+" m "+"is decreasing at decreasing rate";
}









// vti = vt;










else // non uniform speed
{
  title="";
//title="Non-Uniform speed! v = "+dvalue(vt)+ " m/s is always changing";
}

[lookang]

as the user move the green dots T[j], yv[j], how to make they green dots snap to integer values ?

currently the green dots can be any double value which is difficult to use especially if want to explore simple numbers.

for example


i tried change the type to integer but it did not work out.

yv[j] to int but they moved aside to

any tips ?

[Fu-Kwun Hwang]

Define a variable e.g. id and set property "element" for particleSet to id.
When user drag one of the particle, the id will contain the index for the particle.
id will be -1 if none of them were dragged.

if the position of y is yv (which is an array).
set up OnDrag property as following

if(id>-1) yv[id]=(double)((int)yv[id]); // this should work
You can add similar code to others.

 (int)yv[id] will change the type to integer , so the value will be truncated.
But yv[id] is a double so we need to change the type back to double.

yv[id]=(double) ( (int)yv[id]);

[lookang]

ok i try, i think ur method is neater than the one i did in weexvrelation06.xml
working on 2 files now.

i like the interface of weexvrelation06.xml, but i thought got bug so i moved to weexvav10.xml.

i like the programming of weexvav10.xml as i have recently spent my time here.

[lookang]

Define a variable e.g. id and set property "element" for particleSet to id.
When user drag one of the particle, the id will contain the index for the particle.
id will be -1 if none of them were dragged.

i followed the "set property "element" for particleSet to id."

but i monitor the value of id, it is always zero.

what am i doing wrong

the rest of the code works! but because the "set property "element" for particleSet to id." didn't work, only the yv[0] works now.

[lookang]

no worries, i finally figure out

In Models - Variables
i assign a new variable
j integer type

In Models - Custom
i added a new function called dsnap()

Code:

public void dsnap () {

// for(int i=0;i 
//yv[i] = yv[i] - (yv[i]%1.0); // for future used change %1.0 to %0.5 if want snap to 0.5 :)

 if(j>-1) yv[j]=(double)((int)yv[j]);

In View
Polygon
Point Selected assign that to the earlier declared variable j
On Drag add the new function as follows

Code:

dragvt();
dsnap();

Debugging purpose:
Add a new field, variable j format "j = 0.0"

works now........no to worry!

[Fu-Kwun Hwang]

Yes. You need to define variable in the model. Normally, I will define a variable named "id";

And I will add code like:

Code:

if(id>-1) yv[id]=(double)((int)yv[id]);

in the drag action field.

Please add id>-1 , because id equal to -1 when none of the element was selected.