Tagged Questions
0
votes
1answer
43 views
The units of gain and number of atoms in population inversion in a laser
I am following my university course notes on amplification in laser media, and have come across expressions for the gain of a medium, but the notes are not exactly rigorous... The expression given for ...
0
votes
2answers
138 views
Why metric system uses kilogram as a basic SI unit?
SI system uses all (that I know) measurement basic units as 1 (single) instance: meter, second, ampere, etc, except the KILOgram. It already defined with 1000 multiplier (kilo).
It prevents from ...
0
votes
0answers
28 views
How to convert lb/MMBTU to concentration?
This might be a stupid question but...
I am looking over this document for allowable emissions for PM particles in biomass furnaces.
They are given in lbs/MBTU, pounds per million British Thermal ...
-1
votes
2answers
90 views
What Physical Quantity has SI Unit $kg \cdot m$,? [duplicate]
What is the physical quantity that has SI (System International) unit of $kg \cdot m$ (kilogram meters)?
-1
votes
4answers
588 views
Why there is no “Edison” unit in physics? [closed]
In the popular culture the XIX-XX century competition between Thomas Edison and Nikola Tesla is well-known. The example could be the Prestige movie, where there are some "Edison's agents" who sabotage ...
17
votes
8answers
1k views
Is there a symbol for “unitless”?
I'm making a table where columns are labelled with the property and the units it's measured in:
Length (m) |||| Force (N) |||| Safety Factor (unitless) ||| etc...
I'd like not to write "unitless" ...
0
votes
1answer
196 views
CGS Units to SI Units
This may be a stupid question but I am having trouble getting the same result in CGS units as I would if I used SI units for a unitless calculation.
I have to calculate $E_c=\frac{m_e c\, ...
4
votes
1answer
282 views
$E^2 = (mc^2)^2 + (pc)^2$: What units are used to measure $E$, $m$, $c$ and $p$?
\begin{equation}
E^2 = (mc^2)^2 + (pc)^2
\end{equation}
If I am using this equation to figure out the energy of something, what units would I use? Would it be the metric system? I.e. kilograms ...
1
vote
3answers
164 views
Can you use PCR to make a standard kg?
While reading this question: Why do we still not have an exact definition for a kilogram? , I had a crazy thought.
Using PCR, you make a known number of copies of a DNA strand where the length and ...
2
votes
1answer
243 views
Conversion from natural units to SI
I got questions about converting units from natural system of units to SI.
To be exact, I'm solving the problem in Heisenber interpretation of quantum mechanics, and I'm using Heisenberg equation of ...
5
votes
3answers
180 views
What is a “measure equation” as mentioned by this TeX Users Group guide?
In this TeX Users Group (TUG) document, Typesetting mathematics for science and technology according to ISO 31/XI by Claudio Beccari, the author makes various typesetting recommendations including:
...
3
votes
1answer
213 views
Do the trigonometric functions preserve units?
I saw an exercise where you had to calculate the units of $C_i, i=1,2$ from an equation like this:
$v^2=2\cdot C_1x$ and
$x=C_1\cdot \cos(C_2\cdot t)$
where
$x$ means meters,
$t$ means seconds ...
3
votes
2answers
582 views
Relating milliampere-hours to watt-hours for batteries
I've seen many batteries that are measured in milliampere hours (mAh), while others are measured in watt hours (wh). How can I convert them between each other so that I can actually compare them? It's ...
-1
votes
2answers
2k views
Unit for Impact Force
Forgive me if this is a newb question but I am not a trained scientist, much less a physicist. I'm just curious and would like to know if there's a unit to measure impact force.
I know the newton is ...
6
votes
5answers
892 views
Is anything actually 1 meter long (or 1kg of weight)?
I believe that no real objects are actually (exactly) 1 meter long, since for something to be 1.00000000... meters long, we would have to have the ability to measure with infinite precision. ...
13
votes
9answers
3k views
What is the logarithm of a kilometer? Is it a dimensionless number?
In log-plots a quantity is plotted on a logarithmic scale. This got me thinking about what the logarithm of a unit actually is.
Suppose I have something with length $L = 1 km$.
$\lg L = \lg km$
It ...
0
votes
3answers
147 views
units of measure
This question is rather historical one.
kilometres can be defined in metres, metres in centimetres, centimetres in millimetres.
There must be some elementary unit (like millimetre or smth.) which ...
6
votes
5answers
482 views
Whats the range of dimension exponents in the SI Units system?
I am working on a software library for Units of Measure. To represent dimensions, I need to know the required range of exponents for each of the seven base units (precisely, I need to know the ...
2
votes
2answers
506 views
Fundamental units
Is it right that all units in physics can be defined in terms of only mass, length and time?
Why is it so? Is there some principle that explains it or is it just observational fact?
-1
votes
3answers
276 views
Help getting the distance an object has moved
What is a distance an object went through at the speed of 14hm/min for 6 hours?
I am having problems with conversions.
First, I tried passing 14hm/min to m/s. I did it alright. But now I am unsure. ...
