What is Center of mass?
[[Image:CoG stable.svg|thumb|Diagram of an educational toy that balances on a point: the CM (C) settles below its support (P). Any object whose CM is below the [[wikt:fulcrum|fulcrum]] will not topple.]] '''Center of mass''' or '''barycenter''' of a system is the average position of all the [[mass]] in a [[system]]. In a rigid body, the centre of mass is always in the same place. In a loose collection the center of mass may be in space, as it is in the [[Solar System]]. Also, as planets' [[orbit]]s change slightly, so will the position of the barycenter. A simple way to understand the concept of barycenter is to push a [[supermarket]] [[trolley]]. If you hold only one corner and push, it will only go in a straight line when you push through the centre of mass. Otherwise a turning force is created. This shows that the mass acts as if it were only in one place. The '''center of gravity''' is a closely related term. It is the point where an object can be balanced perfectly by a sharp point holding it up under the object. It is the center of mass acting in a [[gravitation]]al field. == History == The concept of center of mass was first introduced by the ancient Greek physicist, mathematician, and engineer [[Archimedes|Archimedes of Syracuse]]. Archimedes showed that the [[torque]] (turning force) exerted on a [[lever]] by weights resting at various points along the lever is the same as what it would be if all of the weights were moved to a single point — their center of mass. Archimedes was the first person to work out ways of finding the center of mass in various objects. == Relation between the two terms == The center of mass is often called the ''center of gravity'' because any uniform [[Newton's law of universal gravitation#Gravitational field|gravitational field]] '''g''' acts on a system as if the mass ''M'' of the system were concentrated at the center of mass '''R'''. [[Category:Basic physics ideas]] [[Category:Mechanics]] {{math-stub}}