'''Momentum ''' is the "quantity of motion" an object possesses. In classical [[physics]], the linear form of momentum is defined as the product of [[mass]] and [[velocity]]: :<math> \mathbf{p} = m\mathbf{v} </math> Hence, the faster an object goes, or the more mass it posesses, the more momentum it has. Momentum is a [[vector]] quantity, and therefore has both a magnitude and direction. It is important to physicists because it is a [[conservation law|conserved]] quantity, making it useful for solving problems. In common usage, the words "momentum" and "[[inertia ]]" are ~~related~~sometimes used interchangeably. Inertia is the tendency for a body to ~~remain at rest, ~~resist changes in its motion until and unless a force ~~makes ~~acts on it ~~begin moving. That same tendency works when it is in motion~~.

The motion of an object will continue until something makes it change its motion. A railroad car, once it gets going, will continue its motion for a long time, until the tiny forces of friction cause it to slow down and stop. This can take miles. Even putting on the brakes can take up to mile, because there is so much momentum.

~~Momentum is defined in ~~A [[~~Physics~~force]] in the same direction as the ~~product ~~body is moving will increase its speed. A force in the opposite direction will slow it down. A force coming from the side will cause a deviation from straight-line motion. An interesting case of a sideways force is a weight on the end of a string (~~p~~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 bodypossesses angular momentum. Like linear momentum, angular momentum is a vector quantity and is conserved. An object's angular momentum changes only when a [[~~mass~~torque]] ~~and ~~is applied to it. The magnitude of the angular momentum of a particle orbiting some origin (such as the [[~~velocity~~earth]]~~. ~~orbiting the [[sun]]) is given by

:<math> ~~p ~~L= ~~m * v ~~mvr</math>

~~The faster it goes, the more momentum it has. The more it weighs, the more momentum it has. ~~where

~~A force in ~~*'''L''' is angular momentum*'''m''' is the ~~same direction as ~~mass of the ~~body ~~particle*'''v''' is ~~moving, will increase its speed. A force in ~~the ~~opposite direction will slow it down.~~linear velocity of the particle*'''r''' is the distance from the particle to the origin

~~A force coming from ~~The direction of the ~~side will turn it~~angular momentum vector points perpendicularly to the plane formed by the object's orbit, in accordance with the [[right hand rule]].

~~An interesting case of a sideways force is a weight ~~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 ~~end of a string (like the Biblical slingshot used by ~~object's [[~~David~~moment of inertia]] ~~against [[Goliath]]). While the weight is revolving around you~~, and therefore the ~~string is pulling ~~shape and density of the ~~weight toward you - but it never gets any closer! ~~object. ~~This is called a [[centripetal force|centripetal]], or center seeking, force.~~

=== Generalized momentum ===