# Units Definition and 998 Threads

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.

View More On Wikipedia.org
1. ### How to convert units when calculating a dimensionless quantity?

The original quantity is given in this paper: [reference][1], equations: (31-33-34), where ##a(\eta)= \frac{1}{H\eta}##, so I considered in (1) only the constants which share by dimensions to ##P##. Any help is appreciated! [1]: https://arxiv.org/pdf/hep-th/0703290
2. ### Did my textbook make a mistake when writing these units?

Sorry if there are mistakes regarding the post itself, this is my first time posting. This an easy problem to solve, but this isn't what I'm looking for, but first of all, you can plug in the values and solve for ##\omega##, and it equals ##\frac{170 V}{0.87 T(0.0300 m^2)}## = 6513 Hz, my...
3. ### Fundamental quantities and derived quantities

L=Velocity x time here length is directly proportional to time so come is it independent as it should be since it's a fundamental physical quantity
4. ### B Question about units for "area under curve"

Hello everyone, I am curious, suppose you have a function ##f(x)=x^3## and you to find the area under the curve from 0 to x, the area would be ##\frac {x^4}{4}## but this is units of ##L^4## if x is length, but area is units of ##L^2## so what is going on here? The reason I'm curious is I...
5. ### Can You Convert Meters to Kilograms?

Distance and weight are two separate things so....the question cannot be answered?
6. ### Is zero of nothing nothing? If so, would you write units for nothing?

I stumbled over a datasheet of an old pentode where it says, in the english translation: I thought, wow, I am not sure if I wouldn't have written Ug3=0V instead. I am a theoretician in physics but work more as an engineer and teacher. What happens inside of me seems to be the following: The...
7. ### A Correcting units from this physics paper?

Hi all, I've struggled to resolve a units issue in this 1973 paper by Hora: https://www.academia.edu/23774741/Estimates_for_the_efficient_production_of_antihydrogen_by_lasers_of_very_high_intensities From the paper: " The number N_p of pairs produced in a plasma volume V during a time \tau and...
8. T

### How to write Equations and Symbols in the Homework forum?

Homework Statement: . Relevant Equations: . How do I write equations and symbols in the homework statement and relevant equations sections?
9. ### 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...
10. ### 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...
11. ### 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!
12. ### 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...
13. ### 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...
14. ### 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.
15. ### 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...
16. ### 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...
17. ### 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
18. ### 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...
19. ### 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...
20. ### 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...
21. ### 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...
22. ### 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 ##...
23. ### History 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...
24. ### 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...
25. ### 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...
26. ### A Units of Kerr Understanding Mass & Angular Momentum

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...
27. ### 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...
28. ### 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...
29. ### 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...
30. ### 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...
31. ### 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...
32. ### I Converting Units: How to Convert 1.6*10^7 N/cm^2 to kg/cm^2

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
33. ### I The Units of the Cosmological Constant: eV^2

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...
34. ### 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?
35. ### 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...
36. ### 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?
37. ### 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...
38. ### 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...
39. ### 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...
40. ### Stargazing Understanding the Chandrasekhar Mass Units for Relativistic Lane Emden Equations

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...
41. ### 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?
42. ### 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...
43. ### 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.
44. ### Converting Units: A Beginner's Guide

How can I be doing this conversion, could someone explain to me?
45. ### 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...
46. ### I GR: Can Units Tell You if Quantity is Covariant or 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...
47. ### 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...
48. ### 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...
49. ### 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
50. ### 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...