What is Units: Definition and 997 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. PerpStudent

    Question about distance units in relativity

    When one considers (proper time) ΔΤ2 = Δt2 - Δx2 - Δy2 - Δz2, with c = 1, if t is in seconds, are the units of x,y and z necessarily 3x108 meters?
  2. Z

    Molecular Diameter Units: Understanding the Meaning of pm

    Homework Statement I'm reading a worked problem in my "Fundamentals-of-Physics" textbook, and it states Homework Equations The Attempt at a Solution I was wondering what are the molecular diameter units which I have emboldened? What does pm stand for? Thank you
  3. S

    Determine the density of a planet in SI units

    Homework Statement Determine the density of fictional planet in SI units from the information Homework Equations Planets mass 1.28x10^22 Kg divided by radius 1.12x10^3Km = 1.14x10^25 Kg/m3 The Attempt at a Solution My answer seems all wrong, the SI unit should be in Kg/m cubed. Is...
  4. R

    Question about Multiple Stream Mixings into Units

    Homework Statement I'm currently doing some thermodynamic analysis. I don't know where to put this question, but here goes: I have a system that has two streams entering a condenser, and one leaving. I don't know mostly anything about two of the streams. One stream I have fully defined...
  5. A

    Coulomb Energy Unit Conversion: MeV

    I'm having some difficulty resolving the units (unit conversions will be my great un-doing) for calculation of the Coulomb energy between nuclei. Given that \Delta E = \frac{3e^{2}}{5r} (2Z-1) with the value for r in fermis (~10^-13cm), the elementary charge e in coulombs, and Z is...
  6. J

    Why such strange units of measure?

    Why do astronomers and cosmologists prefer to use the Distance Modulus instead of -- rather than in addition to -- Bly (billion light-years) or Mpc (mega parsecs)? Being a LOG10 it distorts relative distances. You can find Bly plotted on a graph (but not specified), and even in studies comparing...
  7. L

    TGM units of measurement (note: unfamiliar notation used)

    The units of measurement of the SI (System International) are commonly used around the world ·· they form a coherent system usable for a variety of branches of science. But.. there's another coherent metric system that may be a better fit for many applications in chemistry and physics. The...
  8. B

    Exploring the Limits: Planck Units and the Singularity of Black Holes

    Do Planck units apply inside of black holes? Are they modified? Or are they irrelevant? If some Planck units remain unchanged and applicable in black holes, which ones would those be?
  9. P

    MHB Are Units and Principal Ideals Related in Rings?

    Firstly, I have a question (irrevelant to the second one) which is: let x,y be in a ring such that xy is a unit. Does this imply that both x and y are units? I know that if one is a unit and the other is a non unit, then the product is a non unit but I was wondering if I could extend that...
  10. B

    Mathematica Mathematica: How to change units od axis

    Hello, I would like to know, how can I change units showed in axis. I would like to change those relative units (20000, 40000...) to μm. The conversional relation is 50 = 1μm, so instead 20000, 40000 i would like to have 400μm, 800μm. I enclose picture where it should be more clear what I am...
  11. C

    Conduction - Heat Equation - Units Don't Add Up

    Conduction - Heat Equation - Units Don't Add Up! Hi there I have what I think/hope is a simple question: I've been working on heat inputs and outputs in inertia friction welds and have managed to produce a net power term (W) as a function of time. I now want to use that in the heat...
  12. JJBladester

    Bernoulli Equation - Units Question

    Homework Statement My book says that each term in the Bernoulli equation (when divided by ρ, has pressure units). I don't see how. Homework Equations The Bernoulli equation for steady, incompressible flow is: \frac{P}{\rho}+\frac{V^{2}}{2}+gz=constant The Attempt at a Solution...
  13. C

    Units assistance for loading of parts

    Hi all, I am building a model in Abaqus and wondered if somone could assist with the units I need to enter. I have built my parts using mm as the dimension, i.e. part is 10 units (mm) wide. (To clarify this can also be entered as metres as in 10e-3, however I chose to be consistent with...
  14. Y

    Difficulty with relativistic units, eV/c^2

    I'm having some difficulty in working with units of mass at the quantum level. This difficulty most clearly manifests itself when I'm doing a Compton scattering problem. Recall that Compton scattering is given by \Delta \lambda =\frac{h}{m_{e}c}(1-cos(\theta )) and that the rest mass of an...
  15. M

    Information Theory - Shannon's Self-Information units

    Information Theory - Shannon's "Self-Information" units Hi, I'm familiar with information and coding theory, and do know that the units of Shannon information content (-log_2(P(A))) are "bits". Where "bit" is a "binary digit", or a "storage device that has two stable states". But, can...
  16. L

    LaTeX Creating Latex Tables with Units Beneath Parameters

    Hello, I'm just wondering is it possible to put the units of a parameter underneath it rather than next to it. My table is pretty long and I could free up space if I could do this. For example, let's say I have Velocity (m/s) I want it to have (m/s) below velocity I can't figure out how to...
  17. M

    [Thermodynamic Application] Convert emision factor => units of grams/joule

    Homework Statement Hello everybody, Can you help me solve this: Coal-burning power plants convert the sulfur in the coal to sulfur dioxide (SO2), a regulated air pollutant. The maximum allowable SO2 emission for new power plants (i.e., the maximum allowed ratio of the mass of SO2 emitted...
  18. Q

    Getting natural units right in particle physics

    Hi guys. I have been a mathematical physicist and have recently been taking great interest in theoretical particle physics. With some effort I can do calculations in the International System of Units (SI) with complete success if I focus very carefully. With the particle physics natural units...
  19. R

    Units in Rings: show 1-ab a unit <=> 1-ba a unit

    Homework Statement Let R be a ring with multiplicative identity. Let a, b \in R. To show: 1-ab is a unit iff 1-ba is a unit. The Attempt at a Solution Assume 1-ab is a unit. Then \exists u\in R a unit such that (1-ab)u=u(1-ab)=1 \Leftrightarrow u-abu=u-uab \Leftrightarrow abu=uab. Not...
  20. R

    Ring problem: nilpotent elements and units

    Homework Statement Let R be a ring with multiplicative identity. Let u \in R be a unit and let a1, ..., ak be nilpotent elements that commute with each other and with u. To show: u + a1 + ... + ak is a unit. The Attempt at a Solution Need to show that u'(u + a1 + ... + ak)=1 for some u'...
  21. A

    Solving E=mc^2: What Units to Use?

    When solving with E=mc^2 what units should I use in the answer?? For example: (if I have an object with a mass of 43kg) E=mc^2 E=(43kg)(299792458m/s)^2 E=3.86464727 × 10^18 Now here's my problem, do I include units of J/kg (joules per kilogram) or eV (electron volts)?? If someone could...
  22. B

    Units of the integral (x=seconds, y=metres)

    Homework Statement I'm plotting a man jumping over a car for maths and I'm trying to find the critical velocity at which the car has to travel for the jumper to make it safeley over the car the man's jump is approximated by the parabola y= -0.0176x^2 + 0.3595x - 0.2794 and restricted by the...
  23. C

    How to deduce the units of hw?

    Hi everyone, in the book of Paul Harrison (Quantum Wells, Wires and Dots, 2nd Ed.), it is said that \hbarω=871.879 meV but it is known that \hbar=6.58214928\times10^{-13}meV so i can inferred that \omega=9.9879927, but i don't know the units of \omega, or how can i deduce what units he used for...
  24. J

    Understanding Units of ln Voltage to Logarithmic Quantities

    If I had a value of 6V and then found the log which is 1.79 (3.s.f) what are the units of this quantitiy? or is it dimensionless? why?
  25. S

    Units in a heat transferred calculation

    I'm trying to do a calculation using: Heat transferred = mass x specific heat capacity x change in temperature q=mc∆T But the value I'm trying to calculate is the change in temperature so I've rearranged the equation to ∆T= q/mc I think the numbers and answer I have are correct, but the...
  26. C

    Units of Force Confusion lb/in

    Hi all, I have a spreadsheet which says failure will occur in my composite piece when a load of 3500 lb/in is applied. If I were to tensile test this piece and the thickness has already been input (0.138 in) does this mean for every inch wide the piece can take 3500lb of force? That seems...
  27. G

    Building a Physics Machine: 6 Concepts, 12 Units

    Hello, I am in Grade 12 physics class and I have been given a open ended project; where we are required to build/create a machine which would involve at least 6 of the physics concepts: ramps, pulleys, levers, transfer of momentum/energy, projectile motion, circular motion, stored elastic...
  28. fluidistic

    Units problem with my Hamilton's equations

    Homework Statement Let the Hamiltonian with canonical variables be H(q,p)=\frac{\alpha ^3 e^{2\alpha q }}{p^3} where alpha is a constant. 1)Given the generating function F(q,Q)=\frac{e^{2\alpha q }}{Q}, find the expression of the new coordinates in function of the old ones: Q(q,p) and P(q,p)...
  29. Q

    Uncertainties of Dimensionless Units

    I have a physics project, but how do I express the uncertainty of a dimensionless quantity? E.g. how do I express the uncertainty of the coefficient of friction? Do I just write 0.403 ±0.02?
  30. J

    What are the units which I should use for these Rayleigh scattering equations?

    Hello there, I am reading this article: http://nis-lab.is.s.u-tokyo.ac.jp/~nis/cdrom/sig93_nis.pdf After chapter 4.2, it mentions some equations for approximating Rayleigh scattering. That is all well, however, it doesn't mention which units of measurement I should use, nor the value of...
  31. J

    Is 2.00 g/cm^3 Equal to 2000 kg/m^3?

    Homework Statement My problem is to determine whether or not my conversion is correct. 2.00 g/cm^3 is = _______ kg/m^3 Homework Equations If I'm not mistaken, 1 cm^3 = 0.000001 m^3 1kg = 1000g The Attempt at a Solution My equation: 2.00 g/cm^3...
  32. J

    Speed Conversion: MPH to m/s - 15m/h-1

    Ok for the life of me i can't remember how you get from say 15 miles per hour (15m/h) to 15mh-1?
  33. Z

    Converting lbm & lbf: Help with Newton's 2nd Law

    I'm a little confused about the conversion between lbm and lbf (mass pounds and force pounds). I'm doing a problem where I'm using Newton's 2nd law to calculate mass flow rate. F= Δ((Mass flow rate)*Velocity) I know my force is 400 lbf and velocity is 40 ft/s so mass flow rate is...
  34. Z

    What Units Are Used in Solid State Physics Equations?

    I'm having some troubles understanding the unit used in solid state physics. In a paper I read \Lambda a \sim 1 where \Lambda is a momentum cutoff and a is the lattice spacing of a crystal. Questions: 1) What kind of units are customarily used in solid state physics scientific...
  35. S

    Units problem in Keplerian equation

    See the arrow in the jpg file. There must be a unit missing somewhere, since a is distance, and is used as the sqrt(a).
  36. Islam Hassan

    What are the fundamental physical units of measure ?

    I was wondering what were the fundamental physical units of measurement, ie those from which all other units can be derived. To my mind, there are only two things which exist in the universe and from which all units of measurement can be derived : space and matter. The reasoning is as follows ...
  37. nukeman

    *SIMPLE slope question on graphic - Units?

    Homework Statement I just want to be 100% sure I got this correct. I have a log graph, and along the x-axis I have diameter (in cm's) and up the y-axis I have period (in seconds). I had to get the slope, which I got, but what are the units of the slope? s/cm ? Homework...
  38. G

    What is g_c? Exploring its Meaning and Units

    What is g_c in pound force. It is said that it is dimensionless It says in my book that in america where they measure acceleration in feet per s^2 we have: 32.1740 \frac{lb_m\cdot ft}{lb_f\cdot s^2} then they say in my book that in SI-units we get: g_c=32.1740\frac{0.453593 kg...
  39. J

    Does the equilibrium constant have units?

    According to my teacher in my chemistry lesson, the equilibrium constant has different units depending on how many moles of reactant and product there are. But the idea of a constant which changes it's units depending on the situation seems a bit dodgy to me, especially as it seems to be related...
  40. A

    I'm having a lot of trouble converting units

    For some reason I can't seem to be able to convert units without getting all mixed up. I can convert feet to inches to cm fine, but I can't convert units in a more complicated problem; for example, converting ft/sec to km/hour. I just get really mixed up and lose track of the numbers. ] I...
  41. K

    Balancing units in size-energy relationship

    Homework Statement Can someone help me balance the units in these equations? They are statistical best fits for product size - energy relationships. Homework Equations 1. P80 = Cl + W*Sl With units substituted into equation: micron = micron + kWh/t * Sl 2. P80 = Cp * W^Sp With units...
  42. S

    How much does it cost to run 300 school buses for 22 days?

    Homework Statement A large school district has 300 school buses. If each school bus is used 3 hours each day, the average speed of the school buses is 15 mi/h, and the fuel economy of the buses is 10 mi/gal. How much does it cost to run these buses in 22 school days if gasoline costs $1.20 a...
  43. J

    Characterizing Units in M_n(R) for Commutative Rings with 1

    Homework Statement Let R be a commutative ring with 1. What are the units of M_n(R)? Homework Equations N/A The Attempt at a Solution If R is a field, then I know that we can characterize the units as those matrices with non-zero determinant (since those are the invertible...
  44. R

    What is the significance of gravitational units in understanding momentum?

    What are gravitational units?? My teacher recently taught us about gravitational units... she said that its the absolute unit multiplied by acceleration due to gravity... I did not understand the significance of this...Please help me
  45. R

    Formula Rewriting for Different Units Help

    Homework Statement Hello. I have a small question... How does one correctly "modify" an equation to work in different units? The equation below gives the boiling temperature of isopropanol as a function of pressure: T = B / (A - log10P) - C Where T is in kelvin, P is in bar, and A= 4.57795...
  46. X

    SI Units question in physics conceptual question

    Homework Statement If speed, v, of an object depends on time, t, according to the equation v = A + Bt + Ct^4, what are the SI units of A, B, C? Homework Equations v = A + Bt + Ct^4 The Attempt at a Solution For this, I've not known where to start, so I've be plugging in the variables...
  47. R

    Why Choose Radians Over Degrees for Measuring Angles?

    What are the advantages to using one system to measure an angle over another. For example why do we measure angular velocity in radians instead of degrees? Are there any intrinsic advantages to one unit over another? Thanks AL
  48. G

    How to prove units when you have logs in an equation

    Hi, What happens when, following a numerical calculation, you have to prove the units but the equation has logs? For example: ln P = (ln z1 - ln z2)/(z1 - z2) So as the RHS will simplify to a number when all values are known you end up with: ln P = x, x being some value so to find P you...
  49. M

    Pipe Schedules: Pressure, Thickness, & Units

    Hi, I am hoping that someone could enlighten me about pipe schedules. I've searched online but there have been conflicting definitions for schedules, where some people refer to it as pressure and some referring to it as thickness. I need a pipe to be able to withstand 70bar of pressure...
  50. Z

    What Are the Correct Units of Coulomb's Constant?

    Coulomb's constant, which appears in Coulomb's Law, contains ε0. The units of ε0 being F/m Are the units of Coulomb's constant therefore F/m ? Thank you.
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