Determining the centre of mass

[Sinister]

Homework Statement

I'm doing my lab and my TA didn't really explain how we obtain the centre of mass.
Basically the lab is you have a ruler and you make it horizontal and measure the force along it using a scale (obviously in Newtons)...

So you measure the distance of the force from the pivot point to the scale and then I calculated the torque ( F x D).. we did this 3 times each with a different value of D and got 3 different torque values... This part of the lab was to determine where the centre of gravity is for the rule. oh and the mass of the rule is 219.6 grams. So I'm confused how we calculate this?

Homework Equations

The torque of gravity is Tg= mg x Xcm where Xcm is the distance to the centre of mass

2) T= F x D Force from the scale times the distance from the pivot point

The Attempt at a Solution

1) first I found the torque exerted by the ruler which was T = F x D
Then I found the torque of gravity... But I do not know how to calculate the centre of mass

 

[Quinzio]

How was the experiment conduct ? you held the rule with your finger at one end and the scale was placed where ?
Make a drawing possibly.

 

[Sinister]

It was balanced by two rods ... one being the pivot and the other just supporting it
hope this helps

 

[Quinzio]

OK, so since the ruler didn't move, the net torque was zero.

Torque exerted by gravity is mgc where c is the distance (center of mass) - (pivot).
-Fd is the other.

So, mgc - Fd = 0

You know d, F, mg,
compute c.

Don't know if this is what you were looking for.

 

[Sinister]

thanks!