About the Analytical Physics constraint writing.

[opeth_35]

About the Analytical Physics constraint writing...

I have added a photo about my problem. My problem is why did we write while calculating constraint values as d/2. you will see on the picture what I am saying, I cannot see the reason of writing d/2

 

[omoplata]

I guess from what I see, that $d$ is the diameter of the disc and $\phi$ is the angle the disc rotated. Then the radius of the disc would be $d/2$. So the length of the string unwound will be radius times the angle rotated, or $\frac{d}{2} \phi$.

 

[opeth_35]

thank you for explaining :)