i am Aiswarya i am doing experiment based on principle of moment aim is to find unknown mass apparatus Theory its based on the principle of moment in rotational equilibrium net torque is zero F1 produce anticlockwise rotation F2 produce clockwise rotation when they cancelled scale become horizontal we know equation of torque=r X F this separation is r1 , with direction outward to left this weight produce force F1 , downward due to F1 , using right hand rule , direction of torque is from the screen ( thumb ) this separation is r2 , with direction outward to right weight of stone produce force F2 , downward due to F2 , using right hand rule , direction of torque is into the screen ( thumb ) T1 is towards you and T2 is opposite at preset bar is horizontal since no weight is acting due to support that point of axis of rotation is center of mass gravity of scale ( at 50 cm ) if at 50cm it is not horizontal its better to add some extra weight on the inclined end may be tie using a thick wire or something to make balancing at 50 cm like this now scale balanced at 50 cm ( its easy for calculation and better result ) we can start experiment at present equilibrium is on 50 cm marking and mass m1 is at 30 cm marking so separation r1=50-30=20cm not marking on CG value of r1=20 cm we can fix m1=100 g weight holder (50 g ) + one extra mass ( 50 g )=100 g now m2 portion is hanging down so we have to reduce r2 ( move m2 close to center ) to aligning the scale horizontally we moved the string close to center now we can check whether it is balanced still not balanced , m2 portion is still hanging below so move little more close to center move little more now m2 portion inclined up so we have to increase r2 ( m2 , move away from center ) here r1 is kept constant always no need to move m1 its a simplest idea to balance easily , and reduce confusion now aligned horizontally position of m2 is 62 cm marking therefore r2=62 – 50=12 cm here m1=100 g at that time corresponding r2=12 cm now taking m1=150 g by adding one more slotted weight of 50 g now m2 portion is inclined up so r2 have to increase ( move away from CG ) now it become horizontal now m2 is at 67 cm marking r2=67 – 50=17 cm when m1=150 g , corresponding r2=17 cm now fix m1=200 g adding one more 50 g weight now try to balance now m2 is inclined up , so increase r2 m2 move away from CG now aligned horizontal position of m2 is at 73 cm marking r2=73 – 50=23 cm like this choose m1=250 , 300 and 350 find corresponding r 2 values now calculations calculate first observation substitute in the equation m1=100 , r1=20 & r2=12 we get m2=166.67 g similarly next set m1=150 , r1=20 and r2= 17 repeat like this for all observations after that find mean value of m2 should convert to Kg ( SI unit )