![]() ![]() Similarly, a moment of force is measured in newton-meters. Using their example, the energy unit joule is formally newtons time meters. This basically means if we measure two things with the same units, they have the same dimensions. Your document defines dimension as "expression of the dependence of a quantity on the base quantities of a system of quantities as a product of powers of factors corresponding to the base quantities, omitting any numerical factor" So these are not quantities of the same kind.ĭimensions are trickier to define. We can't say that the kinetic energy of the ball is more or less than the weight of a particular blue whale. So these two quantities are quantities of the same kind. We can say that the wavelength of red light is less than the height of some building. The temperature of a water bath.Ī Kind of Quantity is a group of quantities that can be compared with each other. To put it more simply it's something you can measure (at least in principle). Quantity is defined in your linked document as "property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference" The thermal energy in this ball is a quantity of the same kind as the kinetic energy of the ball, because we can compare them and decide if one is more or less than the other.Ĭould someone clarify what the relationships between a quantity, a quantity kind, and a dimension? Height and wavelength are quantities of the same kind because we can compare them to each other: the wavelength of this wave is greater or less than the height of some object. The only reason not to is some standards body has chosen to arbitrarily standardize on using the word "kind" instead of "type" for this usage. You could substitute "type" for "kind" and say that height and width are two quantities of the same type, instead of quantities of the same kind. ![]() They aren't "kind of quantities" they are "kinds of quantities". ![]()
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