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Dynamometer: what it measures

Dynamometer: what it measures


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Dynamometer, tool for measure the magnitude of the forces involved. As often happens, words ending with “-meter” indicate objects that have the purpose of quantifying quantities. We have seen it with the barometer, with the hygrometer, with the hydrometer and so on.

The word dynamometer comes from from the Greek: δύναμις, dýnamis, strength, power and μέτρον, métron, measure, and whoever knows this language already knows what we are talking about, but it is not said that he knows the physical principles on which the instruments of this category are based. I'm talking about tools because at least they exist two types of dynamometer, today, digital and non-digital. There are many more models, some now out of use but which are a precious part of the history of science.

Dynamometer: what it measures

It measures the magnitude of a force, which may seem something really difficult or mysterious, in truth the most popular dynamometer is quite simple. It's a spring placed in a plastic or metal tube. If we apply a force, the spring stretches and when it stops "springing" will indicate the intensity of the force in question.

At the basis of this model is the principle of Hooke's law which assures us that the deformation of an elastic material is directly proportional to the force applied to the material itself. This type of dynamometer is defined elastic, there are also those with lever and pendulum, less common. In any case, the unit of measurement of a force can be the Newton, but also the dyne or kilogram weight.

Digital dynamometer

The digital dynamometer it is often also used as an electronic travel scale or for luggage and can be purchased online for 20 euros. Models in common use, not for scientific purposes, have a maximum load of about 45 kg and are immediate to use. And also comfortable if we are one of those who never know if they have packed too heavy bags to be embarked on the plane for the holidays without a surcharge.

Dynamometric beta

A Beta, also called torque wrench, online costs 113 euros and it is a dynamometer that is suitable for more professional uses, certainly not to understand if we have exaggerated with the luggage leaving for a weekend in London.

Dynamometer: physics

From a more scientific and less "holiday" perspective, speaking of dynamometers and forces to be measured, we must take into account that in carrying out the detection compares to an unknown force to other forces of known intensity to get a number that size what we want.

This can happen directly, as if it were a weighing pan, both indirectly, as when the dynamometer is a sort of graduated cylinder with a spring with a free end and a hook allows the system to be rigidly fixed, while the free end remains the one where the force to be measured is applied.

It is then always necessary to have a graduated scale for which it is necessary to carry out a calibration taking as reference the known weight forces, of the sample masses to hang, in practice, reporting the corresponding elongation.

Dynamometer balance

When we are faced with a dynamometer made with scales can be misleading, so it is better to reiterate that this instrument does not measure mass but mass for gravitational acceleration which therefore provides a force, what we call Strength weight and that is not a burden. It is a derived quantity, different from fundamental ones such as weight. The measurements are in fact in Newton and not in Kg!

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Video: Hand grip dynamometer test (May 2022).