Tension Measurement
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Tension
In physics, tension is a force on a body directed to produce strain (extension); it can be considered to be negative compression. It is measured in according units (newton, dynes, pounds-force, etc). Tension is the dominant static force acting on such objects as a vibrating string or a stretched rubber band.
Hooke's law states the relation between the stress on an object and the resultant increase in its length. The modulus of elasticity of a spring or elastic string can be used to calculate the force it exerts under a specific extension.
The word 'tension' is also sometimes used to refer to electrical voltage; this is the usage in the term high-tension line. Colloquially, 'tension' is used to refer to physiological or mental stress.
In music tension is the perceived need for relaxation or release (Sturm und Drang) created by a listener's expectations as well as dissonance, repetition, tempo, a gradual rise in pitch, and other factors.
surface tension
tensile stress
Tensile architecture
External link
http://www.soi.city.ac.uk/~geraint/papers/afm-aisb.pdf A Connectionist Approach to Driving Chord Progressions Using Tension by Andrés Melo and Geraint Wiggins, ''.PDF format''
Category:Force
de:Spannung
es:Tensión
fr:Tension
pl:Naprężenie
sv:Mekanisk spänning
Surface Tension
In physics, surface tension is an effect within the surface layer of a liquid that causes the layer to behave as an elastic sheet. It is the effect that allows insects (such as the water strider) to walk on water, and causes capillary action, for example.
Surface tension is caused by the attraction between the molecules of the liquid, due to various intermolecular forces. In the bulk of the liquid each molecule is pulled equally in all directions by neighbouring liquid molecules, resulting in a net force of zero. At the surface of the liquid, the molecules are pulled inwards by other molecules deeper inside the liquid, but there are no liquid molecules on the outside to balance these forces, so the surface molecules are subject to an inward force of molecular attraction which is balanced by the resistance of the liquid to compression. There may also be a small outward attraction caused by air molecules, but as air is much less dense than the liquid, this force is negligible.
Surface tension is measured in newtons per meter (N·m-1), is represented by the symbol σ or γ or ''T'' and is defined as the force along a line of unit length perpendicular to the surface or work done per unit area.
Dimensional analysis shows that the units of surface tension (N·m-1) are equivalent to joules per square metre (J·m-2). This means that surface tension can also be considered as surface energy. If a surface with surface tension σ is expanded by a unit area, then the increase in the surface's stored energy is also equal to σ.
A related quantity is the energy of cohesion, which is the energy released when two bodies of the same liquid become joined by a boundary of unit area. Since this process involves the removal of a unit area of surface from each of the two bodies of liquid, the energy of cohesion is equal to twice the surface energy. A similar concept, the energy of adhesion,
Tension Headache
Tension headaches, which were recently renamed tension type headaches by the International Headache Society, are the most common type of headaches. The pain can radiate from the neck, back, eyes, or other muscle groups in the body. Nearly everyone will have at least one tension headache in their lifetime.
Frequency and duration
Tension headaches can be episodic or chronic. Episodic tension headaches are defined as tension headaches occurring less than 15 days a month, whereas chronic tension headaches occur 15 days or more a month for at least 6 months. Tension headaches can last from minutes to days or even months, though a typical tension headache lasts 4-6 hours.
Pain
Tension headache pain is often described as a constant pressure, as if the head were being squeezed in a vise. The pain is frequently bilateral which means it is present on both sides of the head at once. Tension headache pain is typically mild to moderate, but may be severe. In contrast to migraine, the pain does not increase during exercise.
Cause
The exact cause of tension headaches is still unknown. It has long been believed that they are caused by muscle tension around the head and neck. However although muscle tension may be involved, there are many forms of tension headaches and some scientists now believe there is not one single cause for this type of headache. One of the theories is that the pain may be caused by a malfunctioning pain filter which is located in the brain stem. The view is that the brain misinterprets information, for example from the temporal muscle or other muscles, and interprets this signal as pain. One of the main molecules which is probably involved is serotonin. Evidence for this theory comes from the fact that tension headaches may be successfully treated with certain antidepressants. Another theory says that the main cause for tension type headaches and migraine is teeth clenching which causes a chronic contraction of the temporalis
Surface Tension
hello folks (newbie here).
I put a provocative statement in the main entry, to maybe get some discussion going.
The problem is that surface tension can't simply be explained by a "net inward force" argument, which is absurd. A net inward force would cause molecules on the surface to accelerate inwards: and bulk liquid would collapse, contrary to observation.
One theory states that molecules on the surface _do_ accelerate inwards, and sort of bounce back. In this view, the surface region is constantly in motion, and much as grains of sand on a rattling surface are.
But this can't be right either, because molecules in the next layer (ie just a bit deeper than the surface proper must experience a net force _out_ of the bulk. And this doesn't happen either.
My personal opinion is that surface tension is too complicated to be explained by classical mechanics of the highschool type, and any attempt to do so just confuses matters.
Real water is essentially quantum; even in the classical view, molecules have a dipole moment and it's not clear whether this moment is oriented into the liquid, out of the liquid, or parallel to the surface.
Just my two cents....comments please!
sorry, wasn't logged in. I've just discovered the four tildes thing.
best
Robinh 21:33, 11 Dec 2003 (UTC)
The "net inward force" idea is, as stated above, wrong.
One way to see how surface tension works is to see that molecules at the surface, being in the potential wells of fewer neighbours than molecules inside the liquid, have higher energy. They will tend to move to a position of lower energy. This process will stop when equilibrium has been reached. Then it is seen that the density of molecules in the surface layer is very slightly lower than in the bulk of the liquid, because some of them moved. They are therefore further apart than the equilibrium position, and that means that there is an attractive force parallel to the surface, between any two molecules. They do not move,
Tension Wrench
A tension wrench is a tool used in picking locks. Typically shaped like a letter "L" (although the vertical part of the letter is much elongated in comparison to the horizontal part), it is used to apply tension to the inner cylinder of a lock, in order to hold any picked pins in place, while the other pins are shifted. The tension wrench is then used to turn the inner cylinder and open the lock.
Some tension wrenches (called "Feather Touch" wrenches, among other names) are coiled into a spring at the bend in the "L", which helps the user apply constant torque. Some users, however, maintain that such wrenches reduce torque control and the feedback available to the user.
When lockpicking is shown in movies and television shows, the tension wrench is almost always omitted. Opening a pin and tumbler lock by imitating the depicted method is impossible, which was presumably why this convention was adopted.
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Tension Measurement
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Tension Measurement
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