Units Definition and 975 Threads

So here is an example of what I am trying to do. We know that div of an E field=p/eo where p=charge density and eo=the permittivity of free space. This equation is expressed in MKSA units. In order to convert this into Gaussian units, we must multiply E by 1/sqare root of 4*pi*eo, and...

Here's my question: Starting from Coulomb's law, show that e^2/(4*pi*epsilon_0) has dimensions of energy times distance. Coulombs law is F=(1/(4*pi*episilon_0))*(q1*q2/r^2) I understand how to convert the units for e^2/(4*pi*epsilon_0), where e is the charge of the electron, to ev * nm...

we could have a thread for talking about Planck units and getting accustomed to them Planck units are basic and everpresent in QG so it helps to develop a feel for them even tho LQG is itself based on a continuum the underlying spacetime is a continuum and it is only the geometric...

What is the experimental system used to determine that an electron has a mass of 0.511 MeV/c*c ? I'd like to learn about methods other than Millikan's oil drop and Thomson's charge/mass ratios. What is the modern way to generate a value with those units?

Google has a neat calculator built into its search box. There is a good summary here: http://www.google.com/help/calculator.html Copy and paste the following queries to see it work: Arithmetic operations: sqrt((3*6/9)^2+7!) Transcendental: 3*sin( 54 degrees ) 2*log ( e / pi )...

If you guys can check the math on these last 3 questions I would be very greatful. Sorry to throw this many questions at you but I've been doing physics 3 days straight now reviewing for my final tomorrow. Any help would be awsome. :approve: 1. How much heat energy is required to convert a...

In my physics class, when we involved friction...the book kept making it a point of "why the coefficient of friction has no units"...the answer was always because it was a ratio. Well.., if F_{friction}=umg then u=\frac{F_{friction}}{mg}, right? So why can't we say that the coefficient of...

How can I show that if \frac{a}{a^2-2b^2},\frac{b}{a^2-2b^2}\in \mathbb{Z} then a^2-2b^2=\pm 1? If you care to see the whole problem, you can find it here: http://www.math.rochester.edu/courses/236H/home/hw12.pdf It's #4 part c. BTW, why is the significance of this "norm map"? I...

Please can someone explain to me how you convert: 10 micrograms per decilitre into miiligrams per litre I think I had some notes on it somewhere but they have gone awol !

would you give a measurement of mometum units? like kg*m/s?

Just wondering how many people here use English units as opposed to Metrical ones. That is, people living in the english world (UK, USA, Australia, Canada etc) Also, in your dealings with either English units or metrical ones, what have you found to be the major shortcomings of the system?

Hi, I got a simple question, "dot product" have units? I mean, if A=(Ax+Ay+Az)N and B=(Bx+By+Bz)(cm/s) , the units of A.B will be N.(cm/s) Thanks, Cali

What units in the physical universe are not arbitrary? E.g. time (as measured in seconds and years) is arbitrary since it's based on the changing orbit of this little planet in some odd solar system on the edge of an insignificant galaxy. Atomic mass is arbitrary since it relies on which...

The National Inst. of Standards and Technology NIST has a fundamental physical constants website http://physics.nist.gov/cuu/Constants/ and until sometime this year what they posted were the 1998 CODATA recommended values (same as those in Physics Today August 2000, or the CRC Handbook of...

Hello, I'm new here. I was wondering if anyone could help me out with some confusion regarding units. My landlady (like most people) wants to save money on power consumption, so she has me installing Compact Fluorescent Lightbulbs(CFLs), which are supposed to save energy. On the package, it...

What the conversion for bar so that I can use it to work out volume and temprature? Whats the units?

I’m installing a central vacuum in another house I just purchased. I’m not sure what I’ll do with it but a little improvement should make it a good investment. Rather than use a factory power unit, I’ve decided to use 4 shop vacuum units in a series-parallel arrangement. The highest...

sorry I am not sure if this is the correct pigeon hole to use. planck dimentions are well known but why are they the smalest possible units? i think it was wheeler that used Planck units in his quantum foam theory, would we have this theory without planck units?

A pi meson has mass of 139MeV/c^2. what is this in atomic mass? HOw do i solve for this? what steps do I need to do, any examples you can give to help me with to solve? Dx :wink:

Units based on c=G=hbar=k=e=1 turn out to be quick and convenient to use, and one can get used to the scales (a point damgo made earlier in the dimensionless units thread). Heres a kind of minimal toolkit for working with them including some handy comparisons with familiar units. E38 ----a...

If somebody wants to know what Planck units are, how do you go about explaining? Can you make them intuitive without too much technical detail? What would your approach to describing natural units to a non-scientist (possibly a little vague as to what hbar and G are)? I want to know any...

Well, i hate to put silly questions on the forums, but i had to do it this time ! Today i was arguing with my Math teacher on wether it is right or wrong to put equality between two different units. For example, to say that : 1 Metre = 3.4 Foot (i am not sure of the number ... anyway !). I...

I have been playing a bit with the units of coupling constants. Instead of setting c=1, h=1 (natural units) it is interesting to set c=1 but still to keep h explicit in the formulae. You may know that in natural units there is a basic difference between electromagnetism and gravity, namely...

dimensionless cosmology---getting rid of units In cosmology and fundamental physics some papers are written in a system where time, mass, and length are dimensionless. It is not that they are using Planck units---they aren't using any units at all. On usenet recently (sci.physics.research)...

this is not to argue or persuade but just to share a calculation. no answer needed unless you particularly like something about it. several websites, eg. NedWright's Cosmology tutorial have formulas for things like the critical density and the estimate that real density is very close to...