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Undo revision 1031889 by Barack (talk)
An interesting case of a sideways force is a weight on the end of a string (like the Biblical slingshot used by [[David]] against [[Goliath]]). When you twirl the weight around above your head, the string is pulling the weight toward you - but it never gets any closer! This kind of force is called a [[centripetal force|centripetal]], or center seeking, force.
An interesting case of a sideways force is a weight on the end of a string (like the Biblical slingshot used by [[David]] against [[Goliath]]). When you twirl the weight around above your head, the string is pulling the weight toward you - but it never gets any closer! This kind of force is called a [[centripetal force|centripetal]], or center seeking, force.
==Angular momentum==
A rotating or orbiting body possesses angular momentum. Like linear momentum, angular momentum is a vector quantity and is conserved. An object's angular momentum changes only when a [[torque]] is applied to it.
The magnitude of the angular momentum of a particle orbiting some origin (such as the [[earth]] orbiting the [[sun]]) is given by
:<math>L=mvr</math>
where
*'''L''' is angular momentum
*'''m''' is the mass of the particle
*'''v''' is the linear velocity of the particle
*'''r''' is the distance from the particle to the origin
The direction of the angular momentum vector points perpendicularly to the plane formed by the object's orbit, in accordance with the [[right hand rule]].
In addition to orbital angular momentum, the earth has rotational angular momentum due to its spin. The equations for calculating rotational angular momentum depend on the object's [[moment of inertia]], and therefore the shape and density of the object.
=== Generalized momentum ===
The definition of momentum can be generalized in [[Lagrangian Dynamics|Lagrangian]] and [[Hamiltonian Dynamics|Hamiltonian]] dynamics, to
<math>
p=\frac{\partial L}{\partial \dot x}
</math>
where L is the [[Lagrangian]] and <math>\dot x</math> is the velocity. In some cases the generalized momentum is the same as the momentum defined above. For example, for a free particle the Lagrangian equals the [[kinetic energy]] and so
<math>
p=\frac{\partial (m\dot x^2/2)}{\partial \dot x}=m\dot x
</math>
as above.
==External Links==
==External Links==
*[http://id.mind.net/~zona/mstm/physics/mechanics/momentum/momentum.html Momemtum]
*[http://id.mind.net/~zona/mstm/physics/mechanics/momentum/momentum.html Momemtum]
[[Category:Physics]]
[[Category:Physics]]