# What is Units: Definition and 990 Discussions

English units are the units of measurement used in England up to 1826 (when they were replaced by Imperial units), which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.
The two main sets of English units were the Winchester Units, used from 1495 to 1587, as affirmed by King Henry VII, and the Exchequer Standards, in use from 1588 to 1825, as defined by Queen Elizabeth I.The English units were replaced by Imperial Units in 1824 (effective 1 January 1826) by a Weights and Measures Act, which retained many though not all of the unit names and redefined (standardised) many of the definitions.
Use of the term "English units" can be ambiguous, as, in addition to the meaning used in this article, it is sometimes used to refer to United States customary units, which have somewhat different definitions, or to Imperial units, the standard units throughout the British Empire and Commonwealth.

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1. ### Other Yahoo! News: Community College units not transferring in California

There's a news report shown on Yahoo! of community college course credits not accepted for transfer-students to the CSU system schools. (These are schools in California.) https://www.yahoo.com/news/waste-time-community-college-transfers-043010995.html ("Other" picked because not sure this...
2. ### I Units of q in Electric Field Equation

Quick and possibly stupid question, but in the equation for calculating the electric field: ##{\mathbf E} = \frac{1}{4πe_0}\frac{q}{r^2} \hat {\mathbf r}## What unit is ##q## in? Coulombs? Although now that I think more on it I suppose it also depends on the units you're using to calculate the...
3. ### Help is needed for converting units of a simple formula

How would you convert a volume mixing ratio [m3/m3] to the units of [molecules/cm3]? The temperature is given to be 293K and the air density is 1 kg/m3. Please help!
4. ### I What are the units of the squeezing parameter?

As I understand it, when the squeezing operator acts on an annihilation/creation operator, a function of sinh(r) and cosh(r) is produced, where r is the squeezing parameter. I've been reading some papers that say that up to '15 dB of squeezing' have been produced in a laboratory. Does this mean...
5. ### How can I convert loss units, dB/mm, to mm^-1

I am trying to simulate mode loss for a waveguide and the units I get for loss are dB/mm, but I want to convert the units to just mm^-1 so I can the absorption (α) value. I am guessing there is a specific value that I need to either multiply or divide my values with, but I'm just not sure what...
6. ### B Units in exponentials and logarithms

Hello, I was in class and came up with the question of: is there any physics formula in which a number with units is part of the exponent of said formula, and if there is how do the units behave? Such as for example (x meters)^(y seconds) Thank you in advance.
7. ### Mathematical Methods Book That Uses SI Units

I'm looking for an undergraduate-level 'mathematical methods' or 'engineering mathematics' book that uses SI units for the purpose of self-study. I've had my eyes on Zill's Advanced Engineering Mathematics, but it seems to use US customary units. So ideally I'm looking for a book that covers...
8. ### Does the term ##ln(k)## have units in reaction based equations?

$$ln{x/t}=lnk +aln[S_2O^{2-}_8]$$ From the above equation,I made a table with the experimental data of the two terms ##ln{x/t}## and ##ln[S_2O^{2-}_8] ##Bur I didn't mention units for them as I had known that even if k had unit,##lnk ## wouldn't have had.But my teacher pointed out...
9. ### Chemistry Units conversion for solution concentration

What are the units for C= p/RT where p is in Pa Would it be Pa J^-1 mol ? and if so, how could I get the concentration in mol/L
10. ### I Why are Planck units considered fundamental?

Why are Planck units considered fundamental ? After all, there is a square root in their expressions. And the value of the Planck mass is 20 orders of magnitude greater than the average values of elementary particles. $$m_{pl}=\sqrt{\frac{1}{2\pi}\cdot \frac{hc}{G}}$$ The order of the value of...
11. ### I Incorrect units when calculating cosmic ray muon flux

I recently performed an experiment that involved using a cylindrical scintillator to detect cosmic ray muons by observing the amount of particles that decayed within 20 microseconds over a long period of time. I'd like to use this to find the flux of muons at my scintillator so that I can...
12. ### I Interpreting solar event flux units

Hi, I wanted to find the number of protons striking a surface area during a solar event and the units provided are: #/(cm^2 s sr). Say I have a 1 m^2 surface area directly facing the sun, how do I use those units to discover the number of protons/s. What is the value of the solid angle to...
13. ### Verify that ## a^{5} ## and ## a ## have the same units digit

Proof: Let ## a ## be any integer. Applying the Fermat's theorem produces: ## a^{2}\equiv a\pmod {2}, a^{5}\equiv a\pmod {5} ##. Observe that \begin{align*} &a^{4}\equiv a^{2}\pmod {2}\equiv a\pmod {2}\\ &a^{5}\equiv a^{2}\pmod {2}\equiv a\pmod {2}.\\ \end{align*} This means ## a^{5}\equiv...
14. ### Find the units digit of ## 3^{100} ## by the use of Fermat's theorem

Consider modulo ## 10 ##. Then ## 10=5\cdot 2 ##. Applying the Fermat's theorem produces: ## 3^{4}\equiv 1\pmod {5} ##. This means ## (3^{4})^{25}=3^{100}\equiv 1\pmod {5} ##. Observe that ## 3\equiv 1\pmod {2}\implies 3^{100}\equiv 1\pmod {2} ##. Now we have ## 5\mid (3^{100}-1) ## and ##...
15. ### Recent history of measurement of 1 kg and other units

I didn't remember the Lavoisier died at the guillotine. The world's roundest object helps solve the longest running problem in measurement -- how to define the kilogram. I knew about the Pt the Pt-Ir standard. I didn't realize that the mass of various 'standards' changed in time...
16. ### Mathematica Function that integrates another function, with units

Velocity as a function of time, defined with units attached (Quantity feature of Mathematica): fnVq[t_ ]:= 2 m/s^2 * t fnVq[5 s] Integrate[fnVq[tt],{tt,0 s, 2000 ms}] 10m/s 4m When we printed above the value and integral, we got the correct results with proper units. Now I'm trying to...
17. ### Coloring each k-th unit in a circle of n units

suppose you write, clockwise, n numbers (or "units", doesn't matter) in a circle. you then color, clockwise, each k-th number. you do this until you've colored all n numbers, or until you've reached an already colored number. let x be the number of colored numbers. i've figured that if...
18. ### A Don't understand the units for the Kerr solution

I was reading this paper, and I got confused: https://projecteuclid.org/journals/communications-in-mathematical-physics/volume-31/issue-2/The-four-laws-of-black-hole-mechanics/cmp/1103858973.pdf It discusses the Kerr solution for the case of { M4 > J2 } where M is mass & J is angular momentum...
19. ### I Which units is this conversion factor for (molar volume)? 0.023901488

I'm getting the wrong results when using an old, undocumented code and just realized there's a number lurking in it that I can't account for. It's: 0.023901488 and it is multiplied with molar volume and pressure. I have searched for a couple of hours but just can't figure out what the units...
20. ### Transition Rate Matrix for 5 Processing Units

Summary: The transition rate matrix for a problem where there are 5 Processing Units A computer has five processing units (PU’s). The lifetimes of the PU’s are independent and have the Exp(µ) law. When a PU fails, the computer tries to reconfigure itself to work with the remaining PU’s. This...
21. ### I Converting density unit ##MeV^4## to SI units

How to transform density unit in natural units $MeV^4$ to SI units $kg/m^3$, Here's my trial: ##MeV^4 = (10^6)^4 ~ eV^4 = 10^{24} ~ eV^4 ##, ## eV = 1.6 * 10^{-19}~ kg~ m^2 / sec^2, ## ##MeV^4 = 10^{24} ~ 1.6^4 * 10^{-40} ~ kg^4 m^8 / sec^8 ## This is not simply ##kg/m^3##! Any help how to...
22. ### The units digit of a triangular number iw ## 0, 1, 3, 5, 6 ##?

Proof: Let ## t_{n} ## denote the ## nth ## triangular number such that ## t_{n}=\frac{n^{2}+n}{2} ## for ## n\geq 1 ##. Then ## n\equiv 0, 1, 2, 3, 4, 5, 6, 7, 8 ##, or ## 9\pmod {10} ##. Thus ## t_{n}\equiv 0, 1, 3, 6, 10, 15, 21, 28, 36 ##, or ## 45\pmod {10} ##. Therefore, the units digit...
23. ### For any integer ## a ##, the units digit of ## a^{2} ## is?

Proof: Let ## a ## be any integer. Then ## a\equiv 0, 1, 2, 3, 4, 5, 6, 7, 8 ##, or ## 9\pmod {10} ##. Note that ## a^{2}\equiv 0, 1, 4, 9, 6, 5, 6, 9, 4 ##, or ## 1\pmod {10} ##. Thus ## a^{2}\equiv 0, 1, 4, 5, 6 ##, or ## 9\pmod {10} ##. Therefore, the units digit of ## a^{2} ## is ## 0, 1...
24. ### I Help with converting units

Im trying to us 1.6*10^7 N/cm^2. this breaks to (kg*m/s^2)/cm^2. I need my units in terms of cm. So can I convert 1.6*10^7 kgm/s^2/cm^2 to 1.6*10^11 (kgm/s^2)/(m^2) then reduce to 1.6*10^11 kg/ms^2. The go back to cm and have 1.67*10^9kg/cms^2
25. ### I The units of the cosmological constant

In natural units, it’s known that the unit of the cosmological constant is ##eV^2##. I don‘t get why in this paper : https://arxiv.org/pdf/2201.09016.pdf page (1), it says the value of ##\Lambda \sim meV^4##, this means ##\Lambda \sim (10^6 ~ eV)^4 \sim 10^{24} eV^4 ##, shoud not the unit ##eV...
26. ### Question about these thermal expansion coefficient units (m/mK)

so I have never seen this unit before. 10^-6m/mK for the thermal expansion (linear expansion). I believe this unit is micrometers divided by mili kelvins?
27. ### B Fundamental Units and Supplementary Units — What are the differences?

Fundamental units are defined as - each of a set of unrelated units of measurement, which are arbitrarily defined and from which other units are derived. while Supplementary units are - Supplementary units are the dimensionless units that are used along with the base units to form derived units...
28. ### Dot product: ##\vec{D} \cdot\vec{E}## in SI units

I'm trying to calculate the electrostatic energy, and I'm wondering what happens when I dot the D-field and E-field, with Si-units V/m**2. This is my equation: D dot E = (-4x(epsilon) V/m**2)(-4x V/m**2) + (-12y(epsilon) V/m**2)(-12y V/m**2) Are the final Si-unit still V/m**2 or V**2/m**4?
29. ### I Looking for a Comprehensive Explanation of Natural Units

Would anyone know of a book or article that comprehensively explains Natural Units? I am looking for a document that explains all the versions of natural units and why, when, and how to use these units. I am looking for a source that provides many examples of how to use Natural Units. I found...
30. ### Why does my sensor show "gaps" every 16 units of resolution?

Hello Gentlemen, I'm not an EE engineer, yet trying to help my colleagues. I would like to get a general feeling of what could be going on. Probably trivial for some of you. Background We have a motor/torque sensor device that is measuring torque values. We get out digital signals for Torque...
31. ### I Replacing the Measurement standards (SI units)

What might be better foundational units given the knowledge we now have and disregarding legacy, human-scale units. Perhaps setting some known constants to be the base unit of 1 in that measure. For example, the second, based on the unperturbed ground-state hyperfine transition frequency of the...
32. ### Stargazing Chandrasekhar mass units

Using Lane Emden and n = 3 (relativistic), I calculate the correct mass -- the Chandrasekhar mass (about 1.4 Msun) The equation goes Mtotal ∝ a3, because at n=3, the density, ρ, cancels out. a2 ∝ K/G = Kg2 → a3 ∝ Kg3. Here K ∝ h c or Kg m3/sec2 and G ∝ m3/Kg/sec2 This implies the mass, Mtotal...
33. ### B Electric flux density and confusion about units

My general understanding of electric flux density is 'electric flux per unit area'. This gives the SI unit N/C. But According the formula of electric flux density, D=eplison*E, the SI unit is C/m^2. How come the dimension in both cases not matching if both are true?
34. ### Inertia units for a synchronous machine

Hello everyone, I'm sorry if this is not the right sub-forum to post this, but this doubt has been haunting me for a while. I've got some rotatory machine -let's say, generic synchronous machine-. Turns out there are typical values for [kg m^2] (inertia) in the 2-10 range; the software I'm...
35. ### Why do programming languages usually not implement number types with units?

In fact, the only programming language I know of that implements something like units is the programming language Frink. In other programming languages, the implementation is left to the programmer, for example C++ can implement this as a class.
36. ### Converting Units: A Beginner's Guide

How can I be doing this conversion, could someone explain to me?
37. ### B Dynamic pressure in pressure units

We all know that a flowing fluid acquires dynamic pressure as a result of this velocity. But the pressure has been known to be the kinetic energy of unit volume of flow i.e. 0.5 times density multiplied by the square of the velocity. I just want to know how to convert that into units that are...
38. ### I Silly GR Question: Can units tell you if quantity is co/contravariant?

Note: My GR is very cursory and rusty. The probability that I say something bogus in stating my question is very high. Thanks for your help in advance! I have a dumb question. I'm only casually familiar with GR, and I have a hard time telling if quantities should be covariant or contravariant...
39. ### Unit calculations - DWI MRI (Stejskal-Tanner)

Ok, so basically my task is to calculate the apparent diffusion D based on experimental data, which is kind of easy, BUT the problem is with unit of b... Gamma is gyromagnetic ratio and can be expressed as: (s*T)-1 or MHz/T --> but I am not so sure, teacher did not specify Delta is the pulse...
40. ### Problem with units? (trying to solve a normalized function)

I'm trying to solve for this in a deuteron problem. But can't seem to get the right answer. The reduced mass of the deuteron is 469.4 MeV, the binding energy Eb is 2.226 MeV and R = 1.5fm. Using hbar = 6.5817x10^-16 eV.s I get Kappa = sqrt((2(469.4)*2.226)/(6.5817*10^-22)^2) = 6.94*10^16...
41. ### I Multiplying Uncertainties in Different Units

I could not find any clear explanation on multiplying quantities with different units while including their uncertainties. For example, how would you compute the following product with their uncertainties? 3.4 Newtons +/- .12 Newtons x 1.7 seconds +/- .23 seconds
42. ### Trouble with units for Spring Constant

I do not understand how in part a, the units for K can be N/m. If Work is in joules which is kg*m^2/s^2 and we are diving by x^2 which is m^2, then m^2 should cancel out and we should be left with kg/s^2. Kg/s^2 makes more sense because in part b when you find the work done you are multiplying...
43. ### Dimensional Analysis and units of time

time = x(min) distance = 1(y) y = unknown units I think the answer should be 1(y)/ Min. This is not correct becase 1(y) is unknown. Any help? I have the answer but am confused
44. ### Trivial question about units (Hans Bethe Small Hole Diffraction)

http://www.physics.miami.edu/~curtright/Diffraction/Bethe1944.pdf Hans Bethe's paper Jackson doesn't take any issue with Hans Bethe's paper as far as I can tell when he references it. That leads me to believe the two sets of dipoles are equivalent and there happens to be an "old school"...
45. ### I Units of trigonometric functions?

What are the units of the trigonometric functions sinus, cosinus etc? If I take say Sin(0.5), what would the units of the output be?
46. ### I'm not sure which units I should convert this to

Homework Statement:: Hello, I have a simple question which goes like this: Medical ultrasound waves travel at about 1392.8 m/s in soft tissue. Higher frequencies provide clearer images but don't penetrate to deeper organs. Find the wavelengths (mm) of 1.7-MHz ultrasound used in fetal imaging...
47. ### Help with Thermodynamics process equations and units

For part 1. I need to find the temperature, I rearranged the equation so that: T = pV/nR (28000000)(0.45) / (28.96)(8.314) This gives me a value of 52331.4 I am unsure where the units I have used in the equation are correct. I have used pa for pressure, or should I be using kpa? this would...
48. ### B Reduced mass to atomic mass units conversion help please

Hello I am trying to understand how to write the reduced mass into atomic mass units but i am confused how it was done. The equation is $$m_1m_2/(m_1+m_2)$$ For two similar masses in my particular case i have: $$m^2 / 2m = 1/2 * m$$ Then to convert to atomic mass units, the book says it...
49. ### Converting Units to Find Density of Unit Cell

I don't understand the ratio [ 1 g / 6.02*10^23 amu] in the following conversion factor: [228.2 amu / 4.75*10^(-23) cm3] * [ 1 g / 6.02*10^23 amu] = 7.98 g/cm3 (This calculation is in a problem where you're finding the density of a unit cell in g/cm3 - though it has nothing to do with the...
50. ### B Units of rigidity

In something I was reading, I saw the "stiffness" of a material measured in Newtons per meter which makes sense to me because something that is stiff would require more force to change its length. In other words, "Stiffness is the number of Newtons required to condense a material by one meter."...