Rotation of Object around it's centre of mass

[mahi.aw]

Hi all I am new here!

can anyone tell me how can i rotate the object around it's center of mass and not the origin of Cartesian co-ordinates(0,0)..

thanks in advance for help..

 

[willem2]

1. translate the object so its center of mass is at the origin
2. rotate it.
3. translate it back.

 

[mahi.aw]

Hi willem thanks for your prompt reply..

It's sounds good...

But if i do like this way i think i need to do more and more calculations,,which ultimately leads to reduce performance of my program..

is there way to rotate it without translating the object center of mass to it's origin??

 

[Quinzio]

Hi willem thanks for your prompt reply..

It's sounds good...

But if i do like this way i think i need to do more and more calculations,,which ultimately leads to reduce performance of my program..

is there way to rotate it without translating the object center of mass to it's origin??

The method it's been suggested is very quick for a computer as it implies something like only 4 multiplications and 6 additions.

Any other method leads certainly to more complex equations.

 

[mahi.aw]

Hi Quinzio,

Thanks for your reply..
But i did not get the idea of 4 multiplications and 4 additions??
could you please elaborate on it?

 

[Quinzio]

Then I think you need the complete formula (this is not the homework section, btw), then you can elaborate it.

$$\left\{\begin{matrix}<br /> {x}'= (x-x_M)cos \alpha - (y-y_M)sin \alpha+x_M<br /> \\ <br /> {y}'= (y-y_M)cos \alpha + (x-x_M)sin \alpha+y_M<br /> <br /> \end{matrix}\right.$$

 

[mahi.aw]

i know that...but i asked just b/c am not using any matrices in calculation..

thanks & regards