# angular momentum

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## angular momentum

MRIThe cross product of the ordinary momentum of a particle and its position vector, running from the axis of rotation to the body whose momentum is being determined.

In absence of external forces, the angular momentum (AM) remains constant; therefore, a rotating body tends to maintain the same axis of rotation. When torque is applied to a rotating body, the resulting change in AM results in precession. Momentum involved in the rotation of a body about an axis is conserved, as is ordinary momentum. Atomic nuclei possess an intrinsic AM known as “spin”, which is measured in multiples of Planck’s constant.

## an·gu·lar mo·men·tum

(ang'gyŭ-lăr mō-men'tŭm)The spin of MR active nuclei, which depends on the balance between the number of protons and neutrons in the nucleus.

## momentum

the 'quantity of motion' of a body or object. A vector quantity.**the product of mass and velocity. The change in linear momentum is equal to the linear impulse.**

*linear momentum***in the absence of external unbalanced forces, the total linear momentum of colliding bodies or objects will remain constant. Commonly applied to racquet/ball impacts.**

*conservation of linear momentum**angular momentum*the product of moment of inertia and angular velocity.

**in the absence of an external moment (torque), the angular momentum of a rotating body will remain constant. Often applied to low-velocity flight (e.g. gymnastics) to explain how a body can increase or decrease angular velocity by manipulating moment of inertia (e.g. by 'tucking').**

*conservation of angular momentum***if, in the absence of an external moment (torque), an object or body is rotating about one axis (e.g. somersaulting) and rotation about another axis is introduced (e.g. tilt), the result will be a rotation about a third axis (e.g. twist) due to the vector nature of angular momentum.**

*trading of angular momentum***can occur from one part of a body to another in the absence of an external moment (torque) (e.g. if one part of a body increases angular velocity, another part must decrease to conserve angular momentum).**

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