# Force - Descriptions

Descriptions

Since forces are perceived as pushes or pulls, this can provide an intuitive understanding for describing forces. As with other physical concepts (e.g. temperature), the intuitive understanding of forces is quantified using precise operational definitions that are consistent with direct observations and compared to a standard measurement scale. Through experimentation, it is determined that laboratory measurements of forces are fully consistent with the conceptual definition of force offered by Newtonian mechanics.

Forces act in a particular direction and have sizes dependent upon how strong the push or pull is. Because of these characteristics, forces are classified as "vector quantities". This means that forces follow a different set of mathematical rules than physical quantities that do not have direction (denoted scalar quantities). For example, when determining what happens when two forces act on the same object, it is necessary to know both the magnitude and the direction of both forces to calculate the result. If both of these pieces of information are not known for each force, the situation is ambiguous. For example, if you know that two people are pulling on the same rope with known magnitudes of force but you do not know which direction either person is pulling, it is impossible to determine what the acceleration of the rope will be. The two people could be pulling against each other as in tug of war or the two people could be pulling in the same direction. In this simple one-dimensional example, without knowing the direction of the forces it is impossible to decide whether the net force is the result of adding the two force magnitudes or subtracting one from the other. Associating forces with vectors avoids such problems.

Historically, forces were first quantitatively investigated in conditions of static equilibrium where several forces canceled each other out. Such experiments demonstrate the crucial properties that forces are additive vector quantities: they have magnitude and direction. When two forces act on a point particle, the resulting force, the resultant (also called the net force), can be determined by following the parallelogram rule of vector addition: the addition of two vectors represented by sides of a parallelogram, gives an equivalent resultant vector which is equal in magnitude and direction to the transversal of the parallelogram. The magnitude of the resultant varies from the difference of the magnitudes of the two forces to their sum, depending on the angle between their lines of action. However, if the forces are acting on an extended body, their respective lines of application must also be specified in order to account for their effects on the motion of the body.

Free-body diagrams can be used as a convenient way to keep track of forces acting on a system. Ideally, these diagrams are drawn with the angles and relative magnitudes of the force vectors preserved so that graphical vector addition can be done to determine the net force.

As well as being added, forces can also be resolved into independent components at right angles to each other. A horizontal force pointing northeast can therefore be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force. Resolving force vectors into components of a set of basis vectors is often a more mathematically clean way to describe forces than using magnitudes and directions. This is because, for orthogonal components, the components of the vector sum are uniquely determined by the scalar addition of the components of the individual vectors. Orthogonal components are independent of each other because forces acting at ninety degrees to each other have no effect on the magnitude or direction of the other. Choosing a set of orthogonal basis vectors is often done by considering what set of basis vectors will make the mathematics most convenient. Choosing a basis vector that is in the same direction as one of the forces is desirable, since that force would then have only one non-zero component. Orthogonal force vectors can be three-dimensional with the third component being at right-angles to the other two.

### Other articles related to "description, descriptions":

Control Point (orienteering) - Control Description Sheet
... of the control points are described on a control description sheet (or clue sheet) ... It is sometimes incorrectly referred to as a "Course Description Sheet" ... For beginners, and the younger competitors, the description is written in a simple text format, but for advanced orienteers the descriptions use symbols (pictorial), in accordance with the IOF Control ...
Line Tree
... trees as actual landmarks in their written descriptions, i.e ... updated, these line trees might remain but are often eliminated from written descriptions, to be replaced with modern metal and stone markers, or even ... enough long-lasting man-made markers for legal descriptions of land swaps in the wilderness ...
Mohanatarangini - Highlights
... kavya written in the classical style, with the conventional eighteen descriptions, the work delves into aspects of eroticism in its treatment of the romances ... The descriptions of Dwaravati(Dwaraka) that the work provides are in ways very similar to those of Vijayanagara under Krishnadevaraya as seen in the accounts of Portuguese travelers ... The descriptions of market places with colourful stalls and demarcated lanes teeming with craftsmen, clients, merchants royal garden parties and glorious descriptions of the palace are all reminiscent of ...
Clinical Descriptions Of Chronic Fatigue Syndrome
... The clinical descriptions of chronic fatigue syndrome (CFS) vary ... to define the condition, with some overlap of symptoms between descriptions ...
Emmeline - Style
... Smith's novels were praised for their descriptions of landscapes, a technique new to the novel in the late eighteenth century ... identity is formed by her encounters with nature, necessitating intricate descriptions of the heroine's mind and surrounding nature ... Smith's descriptions were particularly literary, drawing on Thomas Gray's Memoirs of the Life and Writing of Mr ...

### Famous quotes containing the word descriptions:

The fundamental laws of physics do not describe true facts about reality. Rendered as descriptions of facts, they are false; amended to be true, they lose their explanatory force.
Nancy Cartwright (b. 1945)

Matter-of-fact descriptions make the improbable seem real.
Mason Cooley (b. 1927)

Our Lamaze instructor . . . assured our class . . . that our cervix muscles would become “naturally numb” as they swelled and stretched, and deep breathing would turn the final explosions of pain into “manageable discomfort.” This descriptions turned out to be as accurate as, say a steward advising passengers aboard the Titanic to prepare for a brisk but bracing swim.
Mary Kay Blakely (20th century)