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Re: Zero with units?



I tell my students that zero is not nothing.

Quantities have dimensionality and "carry" units with them. Their value is a
product of a number and those units. The unit for mass is the kilogram. Thus
it is appropriate to say "this object has mass m = 0 kg" (where the "m" is in
sloping type). One might say that, for example, of a photon.

As the lead reviewer of new and revised IEEE standards for adherence to proper
use of the SI and so forth, I would "ding" a standard that said something
silly like
"the potential at this point is 0";
it should be
"the potential at this point is 0 V".
The same would occur with a statement about the resistance of a
superconductor, so this is not a matter of scale or reference point.

Though the magnitude (numerical value) of a quantity may go to zero, it
retains its dimensionality and thus its units.

Jim

On Thursday 2004 September 16 14:33, leinoffs@SUNYACC.EDU wrote:
Hello,

Sorry to join this discussion so late, but I get the digest version of
Phys-L (and don't read them until days later, even so). I appologize if my
point has already been made


Did someone say:
"Since the number 0 doesn't need units for anything, why try to use them?"

I think that it is pretty important to include the units in stating the
value of a temperature, even if the value is zero (e.g. 0 degrees Celsius)
I don't think any of us would have it any other way.

Obviously this is a problem with temperature (and any other quantities?)
since the value of zero on the Celsius and Fahrenheit scales are based on
an arbitrary temperature. Those zero values of temperature do not coincide
and do not represent an "absolute" temperature value.

Stu Leinoff
Adirondack Community College