Physics Help Forum Dimensions

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 Jun 25th 2008, 08:57 PM #1 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 Dimensions Are there only "time", "length" and "mass" dimensions in physics? Are there any examples for which the dimensions are difficult to determine in terms of the three dimensions? What is the dimensions of magnetic flux in terms of the variables above?
Jun 26th 2008, 04:43 AM   #2

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 Originally Posted by werehk Are there only "time", "length" and "mass" dimensions in physics? Are there any examples for which the dimensions are difficult to determine in terms of the three dimensions? What is the dimensions of magnetic flux in terms of the variables above?
You ask a very interesting question, one related to my own research.

The standard view of Physics is that time, length, and mass are the basic units of Nature to which all other quantities have units that can be derived from them. (Well, at least for Introductory Mechanics.) Must we insist on using that system? I see no reason why we can't change it, but we would have to have three other "base" units to take their place. The difficulty in changing these is that the physical interpretation of the different quantities that Physics uses can change slightly. For example, the unit m/s is easily seen to physically be a velocity and we can get a visual picture of what this means. But if we take the units of Joules and momentum (call this unit "p") what the heck does a J/p mean? It is equivalent to m/s, but the interpretation is a lot more difficult to see.

Having said all this, there are other basic units that are used. When we start talking about Electromagnetic units the typical SI unit systems split into a vareity of different unit systems, all of which have some specific reason for existing (usually to make the equations neater.) The MKS system adds the Ampere (A) as a base unit and the system is called MKSA. Don't be confused though: most textbooks use the Coulomb (C) as a base unit, not the Ampere, which is C/s. But as far as I know there is no "MKSC" unit system officially in use.

The CGS system is where the real confusion starts. There are at least four of them in use and unfortunately when you look at a textbook or professional paper, they rarely tell you what system they are using. These systems typically set certain constants of nature to have a value of 1 (and sometimes are defined then to be unitless.) For example, the Heaviside-Lorentz system of units sets $\displaystyle c = \hbar = 1$ to remove the "excess" constants from the equations.

For the record, magnetic flux in the MKSA system is measured in Webers (Wb). This can be expressed in base units as $\displaystyle kg / A m s^2$, or using Coulombs, kg/Cms.

-Dan
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 Jun 26th 2008, 09:58 PM #3 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 What's your topic of research?
Jun 27th 2008, 04:24 AM   #4

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 Originally Posted by werehk What's your topic of research?
It isn't so much a specific topic as it is under the category of Metaphysics. I am looking to see if there is a way to redefine the unit system to work under a completely different set of base units. Specifically we have conservation of energy and momentum so I'm starting with units of Joules and kg m /s as base units. I haven't excluded other possibilities, but the work is very slow going. It would appear that the base units currently employed for Mechanics are pretty intuitive to the human mind; that is to say they are based on our perceptions. This is a part of my general research on units, which can be summed up by the question "What exactly is a unit?"

-Dan
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 Jun 29th 2008, 08:27 PM #5 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 topsquark, I guess in order to have a revolution in the units, there should be some innovative ideas towards the physics knowledge we possess. There must be some new interpretations on ,for example, classcial physics with all those energy, forces. Do you have some new interpretations on them or interpretations in quantum level with all those classical physics?
Jun 30th 2008, 03:21 AM   #6

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 Originally Posted by werehk topsquark, I guess in order to have a revolution in the units, there should be some innovative ideas towards the physics knowledge we possess. There must be some new interpretations on ,for example, classcial physics with all those energy, forces. Do you have some new interpretations on them or interpretations in quantum level with all those classical physics?
That's one of the hangups: I haven't been able to develop one yet.

-Dan
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