What is Center of mass? — Physics

Definition 16.1 High School Physics · Chapter 16 — Forces and Motion

The center of mass of a body or system is its balance point — the average position of its mass: the geometric center of a homogeneous symmetric body; for two point masses, the point of the joining segment at distances in the inverse ratio of the masses, $\frac{d_1}{d_2} = \frac{m_2}{m_1}$ — closer to the heavier.

A thrown wrench at equal time intervals: the wrench spins, but its center of mass (dots) rides a plain parabola.

Examples

Example 16.2 (A lopsided dumbbell)

Balls of $2.0\,\mathrm{kg}$ and $1.0\,\mathrm{kg}$ sit at the ends of a light bar $0.90\,\mathrm{m}$ long. The center of mass divides it in the inverse ratio $d_1/d_2 = 1.0/2.0$ : $0.30\,\mathrm{m}$ from the heavy ball, $0.60\,\mathrm{m}$ from the light one — balance the bar there.

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