# Resources or learning how SI units work?

1. Sep 1, 2014

### mpatryluk

Hi, I'm looking for an in-depth guide/tutorial about how to use and understand SI notation. As it stands, I've realized it's a source of confusion in physics for me because i never took the time to properly learn.

If anyone knows of any resources which would help me to understand it would be greatly appreciated.

2. Sep 1, 2014

### Malverin

http://en.wikipedia.org/wiki/International_System_of_Units

3. Sep 1, 2014

### mpatryluk

I found that page ages ago and keep it religiously open as a means of memorizing the different units themselves.

But as far as explanations for beginners, in terms of the math and principles behind SI, I haven't found wikipedia to be very helpful.

I've looked through some resources online, some with more success than others, but hoped that i may find someone who knows if a killer resource on this forum. If not I'll have no choice but to back go to google.

4. Sep 1, 2014

### Malverin

It is explained where all the units come from and how their values are chosen.
And if that is not enough, may be you need a converting table - the relation between imperial and SI units. Or you need something else?

5. Sep 1, 2014

### f95toli

It is perhaps worth mentioning that there is no "deep physics" in the SI. The units in the SI were chosen primarily to be practical (for use in industry etc) and also in such a way that the units could actually be realized (=could be used to calibrate instruments).
This is e.g. why the Candela is a base unit in the SI, it is obviously not as fundamental as the second and in principle it could be replaced by a derived unit. However, it turns that in practice it is actually quite difficult to come up with a relevant derived unit that can be used for calibration of say light bulbs, this in combination with some lobbying from the light-bulb industry (not a joke) means that it ended up being a base unit.

From time to time the SI is updated to reflect improvements in our ability to measure things.

Hence, the SI is actually a messy compromise between physics, practical considerations and some politics. This is frequently a source of confusion for people who try to understand it.

6. Sep 2, 2014