An Etymological Dictionary of Astronomy and Astrophysics
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Same as → center of gravity, → center of mass, → centroid.

→ center; → inertia.

Tendency of a body to preserve its state of rest or uniform motion in a straight line.

Inertia, from L. inertia "un-skillfulness, idleness," from iners (gen. inertis) "unskilled, inactive;" → inert.

Laxti "sluggishness, inertia."

An ellipsoid used in describing the motion of a rotating rigid body. It is stationary with respect to the rotating body, and is determined by the body's moments of inertia.

→ ellipsoid; → inertia.

Of or relating to inertia.

From → inertia + → -al.

Laxt, adj. of laxti, → inertia

A force arising from the → acceleration of an observer's → frame of reference.

→ inertial; → force.

→ inertial reference frame.

→ inertial; → frame.

The mass of a body as determined from the acceleration of the body when it is subjected to a force that is not due to gravity.

→ inertial; → mass.

Motion free of any force, with constant velocity.

→ inertial; → motion.

1) A periodic motion of a particle that moves, free from external forces, over the surface of a rotating sphere, such the Earth. Inertial oscillations result from the → Coriolis force. For example, a hockey puck launched on a big enough lake in the northern hemisphere would turn to the right (east) and eventually loop back to nearly the initial point (actually west of that point). The time it takes for the huckey puck to return can be computed with the → Coriolis frequency.
2) Meteo.: An anticyclonic (clockwise) rotation in the northern hemisphere, with the Coriolis force providing the → centripetal acceleration with period of 2π/f, where f is the Coriolis frequency. The opposite should occur in the southern hemisphere.

→ inertial; → oscillation.

A → reference frame or coordinate system in which there are no accelerations, only zero or uniform motion in a straight line. According to the special theory of relativity, it is impossible to distinguish between such frames by means of any internal measurement.

→ inertial; → reference; → frame.

Same as → Newton's first law. The → reference frames to which the law applies are called → inertial frames.

→ law; → inertia.

A coordinate system or frame of reference defined in the vicinity of the Earth in which Newton's first law of motion is valid; that is, a non-rotating and non-accelerating reference frame.

→ local; → inertial; → time.

A quantity which is a measure of the inertness of a body in rotatory motion about an axis. It is equal to the sum of the products of the masses of all particles of the body by the squares of their distances from this axis: I = Σm_ir_i², where r_i is the distance of the particle of mass m_i from the axis. Moment of inertia depends only upon the shape of the body and the arrangement of its mass with respect to the axis. For a solid sphere it is (2/5)MR². Moment of inertia is used in place of mass in problems involving rotation. Thus, the → angular momentum is Iω and → angular kinetic energy is (1/2)Iω², where ω is → angular velocity.

→ moment; → inertia.

Any frame of reference in which the law of inertia does not apply, such as in accelerating and rotating frames. For example, the Earth is a non-inertial frame because it is rotating about its axis. But the rotation is so slow that the associated acceleration is negligible compared to other accelerations commonly encountered in everyday life. However, the non-inertial nature of the Earth appears in, e.g., the → Coriolis effect. → inertial reference frame.

→ non-; → inertial; → frame.

The tendency of a body to resist a change in temperature. A body with a low thermal inertia requires very few calories to change its surface temperature. A low thermal inertia material tends to be thermally insulating, so that the surface temperature changes readily, but those changes are not conducted to depth within the material (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ thermal; → inertia.