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.

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  1. S

    Do all elements of the stress energy tensor really have the same units?

    Some people may remember awhile back when I made a thread showing how when I derived the Einstein tensor and the stress energy momentum tensor for a certain traversable wormhole metric, that the units of the energy momentum tensor were not the same for each element and how a couple of the...
  2. Math Amateur

    MHB Units of the set of all Eisenstein Integers

    In Chapter 1: "Integral Domains", of Saban Alaca and Kenneth S. Williams' (A&W) book "Introductory Algebraic Number Theory", the set of all Eisenstein integers, \mathbb{Z} + \mathbb{Z} \omega is defined as follows:https://www.physicsforums.com/attachments/3392Then, Exercise 2 on page 23 of A&W...
  3. Math Amateur

    MHB Describe the units of Z[sqrt 2]

    In John Stillwell's book: Elements of Number Theory, Exercise 6.1.2 reads as follows: ------------------------------------------------------ Describe the units of \mathbb{Z} [ \sqrt{2}] ------------------------------------------------------ Now ... \mathbb{Z} [ \sqrt{2}] = \{ a + b \sqrt{2} \...
  4. Math Amateur

    MHB Proof of Infinitely Many Units of Z[sqrt n] for Eacn Non-Square Natural Number

    In John Stillwell's book: Elements of Number Theory, Exercise 6.1.3 reads as follows: ------------------------------------------------------------------------------------------------- Show that \mathbb{Z} [ \sqrt{n} has infinitely many units for any non-square natural number n...
  5. Math Amateur

    MHB Units of the Gaussian Integers, Z[i]

    In John Stillwell's book: Elements of Number Theory, Chapter 6 concerns the Gaussian integers, \mathbb{Z} = \{ a + bi \ | \ a, b \in \mathbb{Z} \}. Exercise 6.1.1 reads as follows: ------------------------------------------------ "Show that the units of \mathbb{Z} are \ \pm 1, \ \pm i \ ."...
  6. E

    MHB Show the Units of Zn with modular multiplication are a group

    I am trying to do an exercise where I am showing that the set of all elements of $\Bbb{Z}_n$ that are coprime with n form a group under modular addition. So far I have shown associativity, identity, and closure, but I'm having trouble showing the existence of an inverse. I know I can't use...
  7. M

    Find the zero divisors and the units of ##\mathbb Z[X]/<X^3>##

    Homework Statement Find the zero divisors and the units of the quotient ring ##\mathbb Z[X]/<X^3>## The attempt at a solution If ##a \in \mathbb Z[X]/<X^3>## is a zero divisor, then there is ##b \neq 0_I## such that ##ab=0_I##. I think that the elements ##a=X+<X^3>## and...
  8. E

    Units square root of a Newton

    I have a table with several quantities in it, and one of them is \sqrt{T} (T is tension) I have values for this table, and want to put the units next to the values. Something seems off to me about doing this, I guess because they're not integers. Is it correct to say the units are kg1/2m1/2s-1...
  9. Y

    What is its average speed during this 37 s interval? Answer in units o

    What is the magnitude of the instantaneous velocity (speed) of a freely falling object 37 s after it is released from a position of rest? Consider the acceleration of gravity to be 10 m/s2 . Answer in units of m/s What is its average speed during this 37 s interval? Answer in units of m/s
  10. M

    What units are BTU compatible with?

    Homework Statement Im given a problem where I am supposed to utilize the concept of conservation of energy to find an object initial velocity. There is a force that works on an object. They give me the amount of work done in BTU and the other units are in lb, ft/sec, ft/sec^2...Then I...
  11. P

    Units for Coordinates - Understanding the Debate

    I was reading "Time scales in the context of general relativity" Bernard Guinot, and a few other papers whose names I forget, and was surprised that there was apparently some desire by some physicists to give coordinates units. It seems that the current recommended practice is that...
  12. M

    Resources or learning how SI units work?

    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...
  13. marcus

    How would you explain Planck units to layman?

    Suppose you meet a layman who has not even had Freshman-level college physics, but who has HEARD of or read something about Planck units and is curious about them. How would you go about explaining? Maybe it's obvious to some people how to do it, or maybe you have already had that experience...
  14. K

    Why is the Conversion Factor for kg-force 0.1?

    Homework Statement The specific mass of iron doesn´t seem right in the technical system. Iron is about 8[gr/cm3] I know the weight of 1[m3] steel is about 8 tons. Homework Equations The definition of the kilogram-force unit in the tehnical system is the weight of a mass of 1 kilogram...
  15. K

    Geiger Counter Measurement: Sieverts/Hour?

    I have been looking for an answer about what a Geiger counter actually measures. I am puzzled by the claim that it can actually give measures in sieverts/hour, i.e, measure the dose equivalent received by the body. On Wikipedia (Geiger counter article), I read: "a G-M tube can detect the...
  16. N

    What is the Correct Equation for Volume and Its Units in this Physics Problem?

    Homework Statement In the equation dm = δ x 2∏rLdr Where δ = density, and 2∏rL = volume How is it that the volume can be 2∏rL? The units of r is (metres) and the units of L is (metres) which leads to m2 (Area) Should it not be ∏r2L for volume? The Attempt at a Solution...
  17. T

    Multiplication by different units

    Hi, What does N*m mean? What does N/m mean? What kWh mean? What kW/h mean? What does F=m*a mean? I read maybe all articles on web about concepts of multiplication,units,differences.But respondents only starts with some question(You know,what is dividing,but you do not know what...
  18. S

    How did Einstein simplify the units of c?

    Hi, On p.4 of "A First Course in General Relativity", Shutz says that we redefine the units of time so that the new unit of time is the meter, where one meter is "the time it takes time to travel one meter". He then argues that: ## c =...
  19. J

    Wavenumber Units: Standard or Free-for-All?

    Hi there, quick question about units. I know wavenumber can be defined as 1/λ or 2π/λ, the latter sometimes being termed 'angular' wavenumber. Is there an agreed upon way of distinguishing between these two definitions when displaying units on, for example, a graph or paper? I've seen...
  20. K

    What Are the Issues with Using Multiple Units of Energy?

    . Why do we need 12 Units of Energy? When the SI Unit of Energy Joule should be the universal standard. ...It makes absolutely No Sense Scale is no excuse - there are 20 SI prefixes from 10-24 to 1024 1 electronvolt = 0.1602176565 aJ the ground state energy...
  21. P

    How to get rid of units in Partition Function

    Hi guys, I'm studying a classical ideal gas trapped in a one-dimensional harmonic potential and I first want to write out the partition function for a single particle. This, I believe, requires two Gaussian integrations, like so: Z=\int_{-\infty}^{\infty} d\dot{x}...
  22. N

    Water to air heat exchange - imperial units doing my head in

    Hey guys, newbie here and first post. I've got a (hopefully) simple question, but for some reason my brain just isn't working. I'm too used to working with metric, and even though it should be fairly simple, working with imperial units just hurts. Anyway, here's the problem: I have a specific...
  23. Greg Bernhardt

    Electric and Magnetic Units: Definition and Summary

    Definition/Summary Electric and magnetic units have symbols which are (or begin with) a capital letter, but have names which begin with a small letter. The units below (except for eV) are SI units. dim. = dimension; M = mass; L = length; T = time; Q = charge. Units such as A.s^{-1}...
  24. I

    Newbie Questions about Units in Physics Equations

    In an equation like E=mc^2, what are the units? Like, I know c is a constant, but in the equation is it meters-per-second, kilometers per hour, or what? In this, and other equations how do you know what is meant by the letters in terms of their computational value? If E is 500 joules...
  25. E

    Let's talk about geometrized units

    Is there a reason geometrized units convert everything to length? Why not time or something else? This seems odd to me.
  26. E

    Measurable quantites vs Base units

    So here's the familiar SI base units from NIST length mass time electric current thermodynamic temperature amount (mole) luminous intensity Something has been bugging me about this. For whatever reason I am thinking all quantities are calculated by just three on the list -...
  27. B

    18 units too much in one semester?

    How do you guys feel about taking 18 units in a semester? I know its relative to how difficult the courses are (eg humanities vs technical classes). Right now I am planning on taking Calculus 2 (4 units) Physics 1 +Lab (Mechanics) (3+1 units) A computer engineering class digital logic (3...
  28. P

    Significant Figures and Units in Physics Calculations

    Physics has always been my main interest; with more than a mere "favourite subject" label. Therefore I have made it one of my goals to not only be able to solve problems, but also express rigor and detail in my calculations. With regard to solving problems, I have 2 main questions: 1)...
  29. Math Amateur

    MHB Group of units - Rotman - page 36 - Proposition 1.52

    I am reading Joseph Rotman's book Advanced Modern Algebra. I need help in fully understanding the proof of Proposition 1.52 on page 36. Proposition 1.52 and its proof reads as follows: The part of the proof on which I need help/clarification is Rotman's argument where he establishes that...
  30. PsychonautQQ

    Is the Group of Units in a Monoid Always Closed Under Its Operation?

    Homework Statement Theorm 1: If M is a monoid, the set of M* of all units in M is a group using the operation of M, called the group of units of M. My question is this always a "real" group? for example, is this 'group' always closed under the binary operation? Homework Equations...
  31. Math Amateur

    MHB If R is a domain , then units in R[x] are non-zero constants

    I am reading Joseph Rotman's book Advanced Modern Algebra. I need help with Problem 2.21 Part (i) on page 94. Problem 2.21 Part (i) reads as follows: -------------------------------------------------------------------- Let R be a domain. Prove that if a polynomial in R[x] is a unit, then it...
  32. J

    Energy density of the cosmological constant units question

    Hi Everyone! I need a bit of help with the following question please. How does the energy density of the cosmological constant Uλ=ρλc^2 have the required SI units if λ=4∏Gρ/c^2 I know that the energy density of the cosmological constant (Uλ)is essentially dark energy and the SI units...
  33. P

    Can a change in units cancel out G/4π2 in Kepler's third law?

    For two two bodies of mass M1 and M2 in circular orbits of radius a1, a2 about their common centre of mass, the Newtonian modification of Kepler's third law is a3/P2=G(M1+M2)/4π2. Where a=a1+a2. The problem is that I have been told that when using the units of years, solar masses and...
  34. T

    Units being used in the graphs for ψ and radius (in nm) and ψ^2 and ra

    We've just started learning about ψ in the quantum mechanics section of our atomic structure chapter. So while reading, I found these graphs where they used certain units along the y-axis for the graphs for ψ and radius (in nm), and ψ^2 and radius. What units are these exactly? My chemistry...
  35. T

    Specific Heat in Absolute vs Relative Units

    I'm running a simulation on a gas mixture that spits out its Specific Heat in a number of different units. The values for Specific Heat in Btu/lbmolF vs Btu/lbmolR are the same, which confuses me at first glance. I sort of remember in Thermo not having to worry about Btu/lbmolF vs...
  36. gcombina

    Unit Conversions and Mistakes: Understanding the Basics

    Hello, I am having lots of problems with units. I don't know why but I am getting sick of it. I don't know what am I doing wrong. Let me give you an example. I have this problem: A football player kicks a 0.41-kg football initially at rest; and the ball flies through the air. If the...
  37. FysixFox

    A quick question concerning constants and planck units

    Recently I have taken an interest in physical constants (and, through it, an interest in SI units and the upcoming redefinition of the kilogram). I actually have a list of almost all of them now, standard uncertainties included. After a bit, I decided to have a bit of fun messing around with the...
  38. I

    Trying to cancel units out for velocity of transverse wave

    Not a specific question, but I just need help understanding how units cancel out. v = sqrt(force of tension / mass density) Force of tension is in Newtons. Mass density is in kg/m^3 Nt/ (kg/m^3) = (kg*m/s^2)/(kg/m^3) =(I cross multiply here) (kg*m*m^3)/(s^2*kg) kg cancels out...
  39. J

    Symbol help - Mirrors & units question

    Symbol help -- Mirrors & units question Calculate to the nearest 0.1000 degree the diffraction angle of the first order image produced by monochromatic light of wavelength 5890.0 A as the light passes through a grating of 5500.0 lines/cm. WHAT DOES THE SYMBOL 'A' MEAN?? My guess was 1^-10...
  40. Runei

    Leakage Rate Units - Understanding the Basics

    Hello, At my work I'm working with testing the leakage rate of a gas system, and right now I am trying to gain some understanding of it all. However, there are some things which are very confusing to me, in regards to these rates. Searching the internet I find several different ways to...
  41. B

    What are the Units for the momentum of a Photon?

    Homework Statement A photon, a packet of electromagnetic radiation, carries both energy and momentum. Consider a photon with a wavelength of 428 nm in vacuum. A) What is the frequency of the photon? 7.01×1014 Hz CORRECT B) What is the energy of the photon? 4.64×10-19 J C) What is the momentum...
  42. M

    Different units while calculating Acceleration of Rotating Objects

    Question on Acceleration of Rotating Objects: The Physics Textbook I have says that the Acceleration of a spinning object is the Pythagorean-theorum result of sides for Centripetal-Acceleration (toward the rotation center) and Tangential-Acceleration (perpendicular to Centripetal-Acceleration...
  43. D

    MHB Energy to compress a spring 3 units

    Consider a block on a frictionless surface. The force applied the block in the positive x direction is \(F = e^x\) and the force in the negative x is \(kx\) where k is the spring constant. How is the energy required determined to move the block 3 units? I set up Newton's 2nd but I don't think...
  44. evinda

    MHB Finding the Units of the Ring $R=\mathbb{Z}[w]$

    Hello! :D I am given the following exercise and I have some questions :o Calculate the units of $R=\mathbb{Z}[w]=\{ a+bw, a,b \in \mathbb{Z}\} , w=\frac{-1+i \sqrt{3}}{2}$. In my notes is the following solution: We remark that $w$ is a root of $x^2+x+1$ So, $w^2+w+1=0 \Rightarrow w^2=-w-1$...
  45. A

    Arc Length Units: Explained & Solved Problem

    Hello, I solved the arc length for a particular problem. However, what is the unit of arc length if the units of the velocity vs time graph are m/s vs s? I am really confused.
  46. Manraj singh

    Units of loudness of sound, being a subjective quantity

    I am learning sound. My teachers and textbook say loudness of sound is a subjective quantity, it is different for every person, while intensity is the objective quantity. The first section says intensity is a measurable quantity, WHILE LOUDNESS IS JUST A SENSATION. On the very next page they...
  47. S

    Exploring the Smallest Measurable Units: Planck Length & Pi

    Hi all. This is my first time posting so forgive me If I am doing something wrong. I am a year 7 student interested in all types of physics and my question is, if nothing can be smaller than Planck length then wouldn't past a certain point the digits of pi become obsolete? Simply because the...
  48. Jewish_Vulcan

    How do measurement units affect electrical devices?

    1.What do watts do and how do they affect an electrical device like a motor? 2. what do amps do and how do they affect an electrical device like a motor? 3. what do volts do and how do they affect an electrical device like a motor? I understand what these measurment are and how to solve for...
  49. evinda

    MHB Finding Units in $\mathbb{Z}[i]$: Is There More Than $1, -1, i$, and $-i$?

    Hello! :) Let $d \in \mathbb{Z}$ and the set $\mathbb{Z}[\sqrt{d}]=\{ a+b \sqrt{d},a,b \in \mathbb{Z}\}$. I have to find all the units of the ring $\mathbb{Z}[i]=\{ a+bi , a,b \in \mathbb{Z}\}$ I thought that these: $1,-1,i,-i$ are units of this ring..But are there also others?I think not..Am I...
  50. C

    Using Relativisitic Units (where c = 1)

    Homework Statement It's not really an assigned problem, but it was part of one, and it's a concept that I'm not quite getting. Homework Equations In special relativity, energy can be expressed using the equation E^2 = (pc)^2 + (mc^2)^2, or E = \sqrt{p^2c^2 + m^2c^4}. Apparently...
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