rotational inertia

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rotational inertia

physics

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July 13, 2026

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Rotational inertia, also known as moment of inertia, is a measure of an object's resistance to changes in its rotational motion. Just as mass resists changes in linear motion, rotational inertia resists changes in rotational motion.12

This resistance depends on both the object's mass and how that mass is distributed relative to the axis of rotation. Mass located farther from the axis contributes more to the rotational inertia than mass closer to the axis. The formula for rotational inertia ((I)) is derived from the sum of the products of each mass element ((m_i)) and the square of its distance ((R_i)) from the axis of rotation: (I = \sum m_i R_i^2).2

Rotational inertia is a fundamental concept in understanding the dynamics of rigid bodies rotating about a fixed axis, influencing angular momentum and the torque required to change rotational speed.2

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angular momentum
rotary inertia of an object or system of objects in motion about an axis that may or may not pass through the object or system. The Earth has orbital angular momentum by reason of its annual revolution about the Sun and spin angular momentum because…
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rotary inertia of an object or system of objects in motion about an axis that may or may not pass through the object or system. The Earth has orbital angular momentum by reason of its annual revolution about the Sun and spin angular momentum because…
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mechanics
Uniform motion
For Galileo, the principle of inertia was fundamental to his central scientific task: he had to explain how it is possible that if Earth is really spinning on its axis and orbiting the Sun we do not sense that motion. The principle of inertia helps to provide the answer: Since…
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For Galileo, the principle of inertia was fundamental to his central scientific task: he had to explain how it is possible that if Earth is really spinning on its axis and orbiting the Sun we do not sense that motion. The principle of inertia helps to provide the answer: Since…
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flywheel
…flywheel is given a high rotational inertia; i.e., most of its weight is well out from the axis. A wheel with a heavy rim connected to the central hub by spokes or a web (wheel A in the Figure) has a high rotational inertia. Many flywheels used on reciprocating engines…
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…flywheel is given a high rotational inertia; i.e., most of its weight is well out from the axis. A wheel with a heavy rim connected to the central hub by spokes or a web (wheel A in the Figure) has a high rotational inertia. Many flywheels used on reciprocating engines…
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moment of inertia
…physics, quantitative measure of the rotational inertia of a body—i.e., the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force). The axis may be internal or external and may or may not be fixed. The moment…
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…physics, quantitative measure of the rotational inertia of a body—i.e., the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force). The axis may be internal or external and may or may not be fixed. The moment…
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mechanics
Rotation about a fixed axis
…quantity I that expresses the rotational inertia of the rigid body in analogy to the way m expresses the inertial resistance to changes in linear motion. One would expect to find that the angular momentum is given byand that the torque (twisting force) is given by
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…quantity I that expresses the rotational inertia of the rigid body in analogy to the way m expresses the inertial resistance to changes in linear motion. One would expect to find that the angular momentum is given byand that the torque (twisting force) is given by
Read More