Moment (physics) Article Index for
Moment 		Website Links For
Moment 		 

Information About

Moment (physics)
SHOPPER'S DELIGHT
 
Shop For:  
Department
Price Minimum:
Price Maximum:
      



In Physics , the moment of force (often just '''moment''', though there are other quantities of that name such as Moment Of Inertia ) is a quantity that represents the magnitude of Force applied to a rotational system at a distance from the axis of rotation. The concept of the '''moment arm''', this characteristic distance, is key to the operation of the Lever , Pulley , Gear , and most other simple machines capable of generating Mechanical Advantage . The SI unit for moment is the Newton Meter (Nm).


OVERVIEW


In general, the moment M of a Vector '''B''' is

: \mathbf{M_A} = \mathbf{r} imes \mathbf{B} \,;

where

:r is the position where quantity '''B''' is applied.
:× represents the Cross Product of the vectors.

If r is a vector relative to point ''A'', then the moment is the "moment '''M''' with respect to the axis that goes through the point ''A''", or simply "moment '''M''' around ''A''". If ''A'' is the Origin , one often omits ''A'' and says simply ''moment''.


PARALLEL AXIS THEOREM

Since the moment is dependent on the given axis, the moment expression possess a common y,

: \mathbf{M_B} = \mathbf{R} imes \mathbf{B} + \sum_{i=0}{\mathbf{r_i} imes \mathbf{b_i}} \,

where

: \mathbf{B} = \sum_{i=0}{\mathbf{b_i}} \,

or alternatively,

: \mathbf{M_B} = \mathbf{R} imes \mathbf{B} + \mathbf{M_A} \,


RELATED QUANTITIES


Some notable physical quantities arise from the application of moments:

  • Angular Momentum (''L = Iω''), which is typically the cause of rotational motion of a body.

  • Moment Of Inertia (''I = mω×r''), which is analogous to Mass in discussions of rotational motion.

  • Torque (''τ = rF''), which is a Force applied on a position of a body. When no net torque is applied, angular momentum is conserved.



HISTORY


The principle of moments is derived from Archimedes ' discovery of the operating principle of the Lever . In the lever one applies a force, in his day most often human muscle, to an ''arm'', a beam of some sort. Archimedes noted that the amount of force applied to the object, the ''moment of force'', is defined as ''M = rF'', where ''F'' is the applied force, and ''r'' is the distance from the applied force to object.


REFERENCES