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That property of matter which manifests itself as a resistance to any change in the motion of a body. Thus when no external force is acting, a body at rest remains at rest and a body in motion continues moving in a straight line with a uniform speed (Newton's first law of motion). The mass of a body is a measure of its inertia. See Mass
inertia(i-ner -shă) The property of a body by which it resists change in its velocity. It is inertia that causes a body to continue in a state of rest or of uniform motion in a straight line (see Newton's laws of motion). The force required to give a specific acceleration to a body depends directly on its inertia. It is through the property of inertia that the concept of the mass of a body (its inertial mass) arises.
in mechanics, a property of material bodies that is reflected in the first and second laws of mechanics. When there are no external influences (forces) acting on a body or when they are mutually balanced, inertia is manifested in the fact that the body maintains unchanged its state of motion or rest with respect to the so-called inertial frame of reference. If, however, an unbalanced system of forces acts on the body, then the property of inertia is manifested in the fact that a change in the body’s state of rest or motion, that is, a change in the velocities of its points, takes place gradually and not instantaneously. Here, the greater the inertia of the body the more slowly the motion changes. The mass of a body is the measure of its inertia.
The term “inertia” is still used with respect to various instruments; the inertia of an instrument is its property of displaying readings with a certain delay.
S. M. TARG