The si-units tag has no wiki summary.
4
votes
3answers
326 views
Why do we still not have an exact definition for a kilogram?
I read that there is an effort to define a kilogram in terms that can exactly be reproduced in a lab. Why has it taken so long to get this done? It seems this would be fairly important.
Edit
Today I ...
3
votes
2answers
538 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 ...
6
votes
3answers
1k views
coulomb force in SI and cgs
Coulomb force in SI is
$ F = \frac{Q1*Q2}{4\pi\varepsilon R^{2}} $
while in CGS
$ F = \frac{Q1*Q2}{R^{2}} $
why is it? I mean doesn't it any make difference in dimension? since $ \varepsilon $ ...
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 ...
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" ...
10
votes
6answers
850 views
What's keeping us from simply redefining Avogadro's Number / the Mole as a definite integer?
This might be a question to ask in a Chemistry site, but because there is a lot of talk about redefining many units of measurements in terms of Avogadro's Number / the Mole, I was wondering why we ...
5
votes
1answer
230 views
The origin of femto, atto and zepto SI prefixes
Do you know why the SI prefixes: femto, atto, zepto have been accepted by Scientific Community, if this triad of metric units, is neither greek nor latin?
6
votes
5answers
431 views
Why were the SI base quantities chosen as such?
The reasons for choosing length, mass, time, temperature, and amount as base quantities look (at least to me) obvious. What I'm puzzling about is why current (as opposed to resistance, electromotive ...
2
votes
1answer
338 views
How large is the information collected from an inverse femtobarn of collisions?
I ran into this while looking at measures of humongous amounts of data. How does the information (data) collected in an inverse femtobarn exposure compare to a gigabyte of data ?
