Rotational Dynamics

Front

Extended Object Noun

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[ex-tend-ed ob-jekt]

Back

Extended Object

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An object that possesses a definite, non-negligible shape and size, as opposed to a theoretical point mass.

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Example: A baseball bat is an extended object because its size and shape matter; you can't treat it as a single point when it spins or rotates.

Front

Axis of Rotation Noun

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[ak-sis uv roh-tay-shun]

Back

Axis of Rotation

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The real or imaginary straight line around which an object rotates or revolves.

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Example: This diagram shows the Earth spinning on its axis of rotation, an imaginary line running through it, which causes the cycle of day and night.

Front

Lever Arm Noun

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[lev-er arm]

Back

Lever Arm

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The perpendicular distance from the axis of rotation to the line along which a force is exerted.

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Example: This diagram shows the 'Force arm' as an example of a lever arm, which is the distance from the fulcrum (elbow) to where the muscle applies force.

Front

Torque Noun

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[tork]

Back

Torque

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A measure of the twisting force that causes an object to rotate around an axis.

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Example: This image shows how a force (F) applied by each child on a seesaw creates a turning effect, or torque, around the central pivot point (fulcrum).

Front

Net Torque Noun

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[net tork]

Back

Net Torque

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The vector sum of all individual torques acting on an object, which determines its angular acceleration.

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Example: Forces from the steam push on the turbine blades, creating a total turning effect (net torque) that causes the central axle to rotate.

Front

Moment of Inertia Noun

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[moh-ment uv in-er-shuh]

Back

Moment of Inertia

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A quantity measuring an object's resistance to changes in its rotational motion, dependent on its mass distribution.

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Example: This image shows that an object's moment of inertia is low when its mass is close to the axis of rotation (left) and high when its mass is spread out (right).

Front

Angular Velocity Noun

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[ang-gyuh-ler vuh-los-i-tee]

Back

Angular Velocity

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The rate at which an object rotates about an axis, specifying both angular speed and direction of rotation.

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Example: A rotating wheel has angular velocity (ω), which is how fast it spins. This rotation causes the car to move forward with a linear velocity (v).

Front

Angular Acceleration Noun

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[ang-gyuh-ler ak-sel-uh-rey-shun]

Back

Angular Acceleration

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The rate of change of an object's angular velocity with respect to time.

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Example: Applying a force to the edge of a bike tire causes it to spin faster, demonstrating angular acceleration, which is the rate of change of rotational speed.