Line of action
Encyclopedia
In physics
, the line of action of a force
F expresses the geometry of how F is applied. It is the line
through the point at which F is applied and along the direction in which F is applied.
The concept is essential, for instance, for understanding the net effect of multiple forces applied to a body. As an example, if two forces of equal magnitude
act upon a rigid
body along the same line of action but in opposite directions, then they have no net effect—loosely speaking, they cancel one another out. 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.
One practical application of the concept is in animation
and character posing.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, the line of action of a force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
F expresses the geometry of how F is applied. It is the line
Line (mathematics)
The notion of line or straight line was introduced by the ancient mathematicians to represent straight objects with negligible width and depth. Lines are an idealization of such objects...
through the point at which F is applied and along the direction in which F is applied.
The concept is essential, for instance, for understanding the net effect of multiple forces applied to a body. As an example, if two forces of equal magnitude
Magnitude (mathematics)
The magnitude of an object in mathematics is its size: a property by which it can be compared as larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs....
act upon a rigid
Structural rigidity
In discrete geometry and mechanics, structural rigidity is a combinatorial theory for predicting the flexibility of ensembles formed by rigid bodies connected by flexible linkages or hinges.-Definitions:...
body along the same line of action but in opposite directions, then they have no net effect—loosely speaking, they cancel one another out. But if, instead, their lines of action are not identical, but merely parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
, then their effect is to create a moment
Moment
- Science, engineering, and mathematics :* Moment , used in probability theory and statistics* Moment , several related concepts, including:** Angular momentum or moment of momentum, the rotational analog of momentum...
on the body, which tends to rotate it.
One practical application of the concept is in animation
Animation
Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. The effect is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in several ways...
and character posing.