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Tension (mechanics)
 
 
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In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. Tension is measured newton
Newton

The newton is the International System of Units SI derived unit of force, named after Isaac Newton in recognition of his work on classical mechanics....
s or pounds-force and is always parallel to the string on which it applies. There are two basic possibilities for systems of objects held by strings. Either acceleration is zero and the system is therefore in equilibrium or there is acceleration and therefore a net force is present.






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In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. Tension is measured newton
Newton

The newton is the International System of Units SI derived unit of force, named after Isaac Newton in recognition of his work on classical mechanics....
s or pounds-force and is always parallel to the string on which it applies. There are two basic possibilities for systems of objects held by strings. Either acceleration is zero and the system is therefore in equilibrium or there is acceleration and therefore a net force is present. Note that a string is assumed to have negligible mass.

System in equilibrium


A system is in equilibrium when the sum of all forces is zero.



For example consider a system consisting of an object that is being lowered vertically by a string with tension, T, at a constant velocity. The system has a constant velocity and is therefore in equilibrium because the tension in the string (which is pulling up on the object) is equal to the force of gravity, mg, which is pulling down on the object. (Assume up is positive and down is negative.)



System under net force


A system has a net force when an unbalanced force is exerted on it. An equivalent statement is the sum of all forces is not zero. Acceleration and net force always exist together.

For example consider the same system as above but suppose the object is now being lowered with in an increasing velocity downwards (negative acceleration) therefore there exists a net force somewhere in the system. In this case negative acceleration would indicate that | mg | > | T |.

Strings in modern physics


String-like objects in relativistic
Special relativity

Special relativity is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein in the paper "Annus Mirabilis Papers#Special relativity"....
 theories, such as the strings
QCD string

In quantum chromodynamics, or more generally, quantum gauge theory with a connection form which are colour confinement, stringlike degrees of freedom called QCD strings or QCD flux tubes form....
 used in some models of interactions between quarks, or those used in the modern string theory
String theory

String theory is a developing branch of theoretical physics that combines quantum mechanics and general relativity into a quantum gravity. The String s of string theory are one-dimensional oscillating lines, but they are no longer considered fundamental to the theory, which can be formulated in terms of points or surfaces too....
, also possess tension. These strings are analyzed in terms of their world sheet, and the energy is then typically proportional to the length of the string. As a result, the tension in such strings is independent of the amount of stretching.

See also

  • Physical compression
    Physical compression

    Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is tension ....
  • Force
    Force

    In physics, a force is that which can cause an object with mass to change its velocity. Force has both Euclidean_vector#Length of a vector and Direction , making it a Vector quantity....
  • Stress
    Stress

    Stress may refer to:...
  • Tensile strength
    Tensile strength

    Tensile strength , or is the Stress at which a material breaks or permanently deforms. Tensile strength is an Intensive and extensive properties and, consequently, does not depend on the size of the test specimen....
  • Strings (music)
    Strings (music)

    A string is the Vibrating string that is the source of vibration in string instruments, such as the guitar, harp, piano, and members of the violin family....
  • Surface tension
    Surface tension

    Surface tension is an attractive property of the surface of a liquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid ....