Question

define centre of mass

Answer 1

The center of mass is a position defined relative to an object or system of objects. It is the average position of all the parts of the system, weighted according to their masses.

Answer 2

Hii,
Friend here's the answer you are looking for :-
centre of mass refers to the centre of any object which counterbalance the force of gravity acted by Earth on them not to fall on the ground that's why it's essential to maintain your centre of mass while walking and writing anything in the bikes also the engine are the example of centre of mass in car the middle seat and in our body the waistline and the area between belly button is Our centre of mass.
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