In
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
, the line of action (also called line of application) of a
force ''(F)'' is a geometric representation of how the force is applied. It is the
line through the point at which the force is applied in the same direction as the
vector
Vector most often refers to:
*Euclidean vector, a quantity with a magnitude and a direction
*Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematic ...
.
[Mungan, Carl E. "Acceleration of a pulled spool." The Physics Teacher 39.8 (2001): 481-485. https://www.usna.edu/Users/physics/mungan/_files/documents/Publications/TPT.pdf]
The concept is essential, for instance, for understanding the
net effect of multiple forces applied to a
body. For example, if two forces of equal
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
act upon a
rigid body along the same line of action but in opposite directions, they cancel and have no net effect. But if, instead, their lines of action are not identical, but merely
parallel, then their effect is to create a
moment on the body, which tends to
rotate it.
Calculation of torque
For the simple geometry associated with the figure, there are three equivalent equations for the magnitude of the torque associated with a force
directed at displacement
from the axis whenever the force is perpendicular to the axis:
:
where
is the
cross-product,
is the component of
perpendicular to
,
is the
moment arm
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of ...
, and
is the angle between
and
References
Force
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