But every object has a *center of mass* about which all of its mass is equally balanced. If you knew where the center of mass of a given object was located, then you could balance the object on your finger by holding it under that point.

The real importance of the center of mass is that the force of gravity, and all inertia forces, can be modeled as passing through the center of mass. No matter how unevenly the mass is distributed throughout the object, the total weight of the object can still be described as acting through the center of mass. Once the center of mass has been computed, it simplifies calculations tremendously.

For symmetrical objects that are made of a single material throughout, the center of mass is simply the center of the object. But irregular shapes are more difficult. Virtual Car must compute the center of mass of *any* body shape that you draw, no matter how irregular it is.

This is done by dividing your shape into many strips. The weight of each strip (based on the density and thickness of the material that you have specified) is then computed, and multipled by its distance from the left corner of the shape. This product is called the *weight moment* of the strip. This process is repeated for all of the strips. A running total is kept for the combined weight of all strips, and the sum of the weight moments for each strip. After all strips are examined, the center of mass is computed, by dividing the sum of the *weight moments* by the total *weight* of all strips. This whole process yields only the *x-coordinate* of the center of mass!

To get the *y-coordinate* of the center of mass, the same process has to be performed using *horizontal* strips, as if the object were turned on its end, and gravity were acting horizontally.

The center of mass is denoted by the symbol .