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# What is the Dyne?

John Lister
John Lister

The dyne is a measure of force. It represents the amount of force required to increase the speed of an object with a mass of one gram, by a rate of one centimeter per second, in the space of one second. For example, if a one gram object was moving at three centimeters per second, it would take one dyne of force applied for one second to increase the object’s speed to four centimeters per second.

The dyne is used as part of a measurement system which uses the centimeter, gram and second as the primary units of length, mass and time respectively. This system was one of the earlier metric systems and dates back to the 19th century. Eventually people found that these units were too small for many common measurements, such as the height of a house. Making such measurements in centimeters or grams produced numbers so large as to be unwieldy. The system was replaced by one using meters and kilograms, which developed into the SI system used today. The most common use of the dyn is in surface tension, which may be seen in the way water from a dripping tap will spread across the opening of the tap and stretch until it falls in a drop.

As an example of how much of a difference this makes, the primary unit for measuring force today is the newton, named after scientist Isaac Newton. One newton is equivalent to increasing the speed of an object with a mass of one kilogram by a rate of one meter per second in the space of one second. One newton is the same amount of force as 100,000 dynes.

The dyne is usually listed using the symbol “dyn,” in the same way that “kg” represents a kilogram. Its name derives from dynamis, the Greek word which means power or force. This means it shares its linguistic origin with words such as dynamo. The dyne has been replaced by the newton, named after Isaac Newton.

The most common use of the dyn is in surface tension. This is the effect by which a liquid pulls itself together to have the minimum possible surface area. One example of this is the way water which lands on a flat, non-permeable, surface will form itself into spherical drops. Another example is the way water from a dripping tap will spread across the opening of the tap and stretch until it falls in a drop. Surface tension can also be seen in the water strider, an insect which is able to exploit surface tension by effectively gripping the surface of the water with its feet, thus walking on water.

Surface tension is measured as force along a horizontal line. The most common, and standard, way to measure this is in newtons per meter. However, in some cases people will express the surface tension in the form of dynes per centimeter. While not standard practice, using dynes can be more practical in such cases as the figures may represent only a tiny fraction of a newton per meter.

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