16 what is centre of mass? derive an expression for the centre of mass of a two particle system.
Answers
When a rigid body undergoes translational and rotational motion simultaneously, we can consider the motion of the rigid body as a combination of a trajectory of a special point in the rigid body due to translational motion only plus a rotation about that point due to rotational motion only. That speial point is called the centre of mass.
let the two particles m1 and m2 are located at position r1 and r2. Then the posistion of centre of mass m is given by
begin mathsize 12px style r subscript c m end subscript space equals space fraction numerator r subscript 1 m subscript 1 plus r subscript 2 m subscript 2 over denominator m 1 plus m 2 end fraction
x subscript c m end subscript space equals space fraction numerator x subscript 1 m subscript 1 plus x subscript 2 m subscript 2 over denominator m 1 plus m 2 end fraction space semicolon space space space space space space y subscript c m end subscript space equals space fraction numerator y subscript 1 m subscript 1 plus y subscript 2 m subscript 2 over denominator m 1 plus m 2 end fraction end style