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. G

    Mean free path in units g/cm^2

    Hello. I have just read a mean free path (a distance) written in units g/cm^2. How do you interpret this unit in terms of the usual idea of the mean free path as a distance?
  2. A

    Units of Measurement for Railcar Operating Loads

    Hi everybody! Would someone please advise on the following matter. I'm making up a table of railcar operating loads. One of the column includes abbreviated units of measurement such as kN, MN, N/mm2, etc. The question is: How should I title the column? I was thinking about titling it...
  3. M

    Matlab FFT Units: Solving the Mystery

    I was browsing another topic, and I suddenly remembered that I've never quite figured out what units matlab's fft returns. I've used the fft before and found where I had signal noise by taking the power density of the Fourier coefficients, which is all I really wanted to use the fft for in the...
  4. A

    Units in the Navier-Stokes equation

    First post; I am starting to read the official problem description of the http://www.claymath.org/millennium/Navier-Stokes_Equations/navierstokes.pdf" and am having trouble understanding the units involved in the first equation :rolleyes: The equation, verbatim, is \begin{equation}...
  5. M

    Converting between units for thermal conductivities (BTUs involved)

    The thermal conductivity of wood is 1 BTU per hour, per square foot, for a temperature gradient of 1 F° per inch. Convert this to units of W/mK, knowing 1 F° = 5/9 C° 1 inch = 0.0254 m 1 foot = 0.3048 m 1 lb = 0.453593 kg 1 kcal = 4184 JI know there are conversions between BTU and...
  6. M

    Finding Infinite Units in \mathbb{Q}(\sqrt{21}) Using Continued Fractions

    How do you find an infinite number of units of \mathbb{Q}(\sqrt{21}) using the \sqrt(21)? I saw one example using continued fractions but do not know how to apply it in this case. I do have the periodic form of the continued fraction of \sqrt(21).
  7. 1

    MATLAB Matlab Pwelch: Changing Units of Plot - Urgent Help

    Hi, I am simulating vibrations in simulink and processing my results in matlab. I am trying plot the PSD for my acceleration results using pwlech method. When I plot the PSD plots from the methods below (NOTE:I have a sampling rate of 0.006 so that means I am using a sample frequency of...
  8. S

    Find all units in each given ring

    Homework Statement Describe all the units (if any) in each given ring: 2Z X Z with addition and multiplication by components; and Z X Q X Z with addition and multiplication by components Homework Equations The Attempt at a Solution I do not know how to begin, I am not sure how...
  9. Femme_physics

    Units for moment of inertia of a circle

    We've always been using mm^4, but I see in my answer book (answer written below) that one solution says R^4. Is it the same thing, just that R^4 is used for a circle? The measurement in my exercise are in mm. I did get the answer, I just wasn't aware I was supposed to write it in terms of R^4.
  10. P

    Units confusion in calculations

    Can someone please explain how kg x kg-2 (in superscript) can equal kg? I hope it does or my calc is wrong! Anywhere I can revise this kind of thing? Mick
  11. E

    Counterexample for Subring and Units Statement

    Hi, I am trying to find a counterexample to disprove this statement, but can't find any: If S is a subring of a commutative ring R, then U(S) = U(R) \cap S Note that U(X) denotes the set of all the units of a ring X, where x is a unit if x has an inverse in X, such that x times its inverse...
  12. A

    Units of measure for Electric and Magnetic Fields

    I'm going in circles on units (or perhaps more accurately different unit systems). The two my professor has chosen to work in are Gaussian units and MKSA units. My problem is one of lack of understanding; are the units of measure for electric and magnetic fields in these systems: Gaussian: E...
  13. A

    Cancelling out units in an equation

    Hi i have done all the work for this problem calculating viscosity and i come to the last part where i need to manipulate and cancel out units to come to a final solution. The equation works out as viscosity = 0.0042m^2 x 9.8m/s/s x 11,401.4kg/m^3 all divided by 1.034466m/s viscosity is...
  14. W

    Error in my units, and I don't understand why

    Homework Statement Let's consider the a piece of a meteor falling to earth. The gravitational acceleration is experiences if GM/r^2. If I integrate acceleration as a function of r, i should get velocity as a function of r, right? \int \frac{GM}{r^2}dr=GM\int...
  15. Philosophaie

    What Are the Time Units for Mean Anomaly Calculation?

    M(t) = M0 + n (t - t0) where M(t) = the Mean Anomaly at time t; M0 = the Mean Anomaly at the Epoch time; n = (G*(Me+Msat)/a^2)^.5 = the satellite orbit's Mean Motion; t = the chosen prediction time; and t0 = the Epoch time. My question is...
  16. R

    Convert Magnetic Field [MMaxwells*N] to Gauss

    Hello, I have a magnetic field in [MMaxwells*N] (Megamaxwells per turn) and I need to convert it into Gauss. I'm not sure how to. Help would be appreciated.
  17. L

    Question about units for arcsecond

    Homework Statement I need to find the diameter of an object in the sky, which i did, but not sure about the arc second. I convert it into degrees wondering how i would remove the degrees. Homework Equations d=2Dtan(a/2) The Attempt at a Solution where D is distance a is angular...
  18. L

    Why Are Radians Used in Calculating Tangential Speed?

    Just calculated the Tangential speed that music is detected from a CD. I found it using Vt=r\omega where r was in meters and \omega I converted from revolutions per second to radians per second. What unit of measure is tangential speed in? Thanks, Leah
  19. T

    Unit Converter: Bq/cu.cm to Bq/L

    excuse me. How converts Bq/cu.cm to Bq/L? tnk.
  20. H

    The Importance of Units for Zero Values in Physics

    My teacher recently docked me 6% on a test because I failed to put units on two values that ended up being zero. For as long as I can remember an answer that is zero does not need units. I looked up examples in our textbook and they left units off answers with values of zero as well. I was...
  21. K

    Converting from hbar = 1 to physical units

    Hi, Hopefully this should be a simple and quick question. I've seen many calculations done with \hbar = 1. If I want to convert back into physical units, what is the corresponding transformation? I know wiki gives a description of...
  22. X

    Troubleshooting Units in Energy Balance Problem

    I do not want to post the entire homework problem as I understand all of it except this one part. The problem deals with energy balance and it states that water is flowing through a nozzle. (From a bigger cross sectional area to a smaller one.) I am trying to calculate the energy of the...
  23. I

    This should be easy Units of log graph?

    I have a question that sounds easy but as of yet no one has been able to give me a satisfactory explanation. I made a plot of mobility (cm^2/Vs) against temperature (K), i then wanted to find an expression that showed the relationship between the two. What i did was took the natural logarithm of...
  24. M

    Converting 1.8uN to g Units: How Many G's Does This Equal?

    this problem might be extremely simple but the wording is confusing me b]1. Homework Statement [/b] "What dose that force correspond to in equivalent acceleration in g uints? (9.81 Nt/Kg)" the force i had from the question be fore is 1.8uN (micro) soooo is it asking me how many g's...
  25. C

    Optical Spectrum Analyzers - Confused on Units

    Hi! I am new to these, and off the bat am confused by the units. Manufacturers quote resolution either in units of length, e.g. 0.04 nm, or HZ. For example, 0.04 pm / 5MHz 0.16 pm / 20 MHz 0.8 pm / 100 MHz. I am thrown by this since I thought frequency was the inverse of...
  26. Femme_physics

    If Moment of Inertia units are mm^4, how do you use it in calculations?

    So, we learned that the units of Moment of Inertia are mm^4. My question is how do they use moment of inertia in static calculation (where we use Newtons), if Moment of Inertia is in mm^4?
  27. C

    Is space made up of individual units?

    Greetings, Is space made up of individual units like pixels on a computer screen? And the amount of space in the universe is increasing? If so, I'm curious how to calculate how often a new pixel comes into existence between any two existing pixels? Or if a new pixel comes into existence every...
  28. M

    Nilpotent, Idepmpotent, units in a ring

    Homework Statement Determine the nilpotent, idempotents and units in a) F[x]/<x2-x> b) F[x]/<x2> Homework Equations The Attempt at a Solution How do I do this without a specified Field? For a) the elements in R would be {a+bx: a,b are in F; x2=x} b) {a+bx: a,b in F; x2...
  29. B

    Understanding Atomic Units for Beginner Mathematicians

    Hi, I know nearly nothing about physics, I'm a mathematician working on a computer program. Anyway, I have to write a program and my boss suggested that I use atomic units and that at the end of the program I can "scale up" to natural units if desired. I tried to read up on these units, but...
  30. F

    Understanding the Unit of θ in the Equation ΔT = Pθ

    Homework Statement In the equation ΔT = Pθ, P is power in Joules per second and ΔT is the temperature difference in °C. Use dimensional analysis to find the unit of θ. Hint, Joules has units of Force time distance. My question is: I don't understand what they mean by finding the unit of θ. Are...
  31. F

    What is the unit conversion for ML^-2T^-1?

    Homework Statement find the units for this equation: ML^-2T^-1 Homework Equations The Attempt at a Solution We were given the answer as kg m^2/s^3, but I just cannot figure out how to arrive at that. I thought the answer was kg/m^2s
  32. BWV

    Correct units to derive Ryberg Constant in ev

    Putting together a spreadsheet to calculate the hydrogen spectrum, cannot seem to get the right mix of units to get the Rydberg constant of 13.605... eV also, what is the significance of R (1/n^2-1) converging to R as n gets large? can anyone put this together or refer me to a source that...
  33. M

    MathCAD error matrix has wrong units?

    Homework Statement ***I Figured out my problem*** If you know how I can delete this thread though, let me know :) I am attempting to run a calculation in MathCAD but I am having trouble. I am getting an error message stating that a value has multiple units when it should be unitless, but I...
  34. C

    The units of a cartesian product?

    Find all units in Z12 X Z6 and their inverses. What i did was find the units of Z12 which are 1,11,5,7 then the ones of Z6 which are 1,5 and take the cartesian product of those two sets?
  35. S

    Wide Range Strain Indicator Units

    In lab for our final project, we used a Wide Range Strain Indicator connected to strain gages on a part we machined to function as a scale. The Indicator device was much like this one: http://www.datasheetcatalog.org/datasheet/vishay/3800.pdf What units would the numbers be that we're...
  36. Femme_physics

    Are work and moment the same thing? They both have the same units

    Moment is Newtons per meter, and work is Newtons per meter. I'm confused as to how to relate them. Are they essentially the same thing?
  37. S

    Converging the Hamiltonian in Atomic Units?

    Homework Statement So the question is I have to use some trial function of the form \sum c_if_i to approximate the energy of hydrogen atom where f_i=e^{-ar} for some number a (positive real number). Note that r is in atomic unit. Homework Equations Because r is in atomic unit, I think I should...
  38. J

    What units are used after eV, MeV, GeV, etc, are divided by c^2?

    I know that the mass of subatomic particles is usually given in electronvolts, and that c^{2} is set to 1 so that we can say, "This particle has a mass of 13 eV." However, if you divide 13 eV by c^{2}, you get an answer, x. What units is this in? Oh, also, what units do we use c in in the...
  39. T

    Units of Charge, ke*Q, -ke*Q/R, 2*ke*λln R & -2*ke*λ

    Homework Statement 1) What are the units for the charge, Q? 2) What are the units for ke*Q? 3) What are the units for - ke*Q / R, R=radius (m) 4) What are the units for 2*ke*\lambda*ln R 5) What are the units for - 2*ke*\lambda 2. The attempt at a solution 1) C, Coulomb's 2) N*m2/C...
  40. J

    Transmission Spectrum- Absolute units?

    Homework Statement In manipulating transmission spectrum data from GaAs and InP I'm told to "Look up the refractive indices of GaAs and InP in the region of  = 1.0 micron, and use these to correct your experimental data for reflective losses and plot the corrected transmission T’ in...
  41. I

    What is meant by density in units of critical density?

    what is meant by density, such as the baryonic matter density in cosmology, in "units of the critical density"? its mentioned in a question i need to do but i don't really know what it means.
  42. J

    How Do You Convert Cubic Centimeters to Cubic Meters?

    How many cubic meters are in 5.43 x 10^6 cm^3? There are .001 meters in the centimeter. m= meter cm= centimeter This is what I did: 5.43 x 10^6 cm^3 (.01m/1 cm)^3 And then did the calculations, which gave me: .0000043 x 10^6 m^3 or 4.3 m^3. Not sure if I set up the...
  43. N

    Why Do Units on Plank's Constant Include Mass, Length, and Time?

    The units on Plank's constant is m^2 * kg / s I'm new to all of this stuff so... Why?
  44. P

    Pressure to Force to Mass with English units

    Homework Statement A pressure of 3000atm is measured with a dead-weight gauge. The piston diameter is 0.17in. What is the mass in pound-mass (lbm)?Homework Equations 1) P=F/A 2) F=PA 3) F=mg 4) F/g=mThe Attempt at a Solution I first used the given diameter to find the cross-sectional area of...
  45. M

    What are the units for effective mass in the formula m* = (h/2pi)2(d2E/dk2)-1?

    Are the units for effective mass in kg? I have been trying to wrap my head around the concept then realized I wasn't even sure about the units. The formula is: m* = (h/2pi)2(d2E/dk2)-1 the units of h are in J-s, and the units of E are in J so... (J-s)2/J = J-s2 J = kg m2/s2 kg m2 s2/s2...
  46. Z

    What is the Corresponding Temperature on the Centigrade Scale?

    Homework Statement A thermometer has its lower and upper fixed points marked as 10 and 80. When it reads 40, what is the corresponding temperature on Centrigrade scale? The Attempt at a Solution I have no idea of solving such type of questions.
  47. L

    Units used on Voyager golden record

    I would like to understand how units of distance, time and mass are defined on the golden record on Voyager spacecraft . I suppose the units are similar to natural units (speed of light=Planck constant=1), except that the basic unit is not GeV: The unit of energy is the energy...
  48. K

    Units in R[x]: A Comprehensive Definition

    Homework Statement Define the set of units in R[x] where R is a commutative Ring and R[x] the polynomial ring.Homework Equations Unit: X is a unit in R if there exist a Y in R such that XY=1The Attempt at a Solution At first I thought it was this: R[x]* = {u +a1x + a2x^2...anx^n : u2=1 and ak2...
  49. M

    Rings- units, nilpotents, idempotents

    Homework Statement Find the units, nilpotents and idempotents for the ring R = [\Re \Re] [0 \Re] (Those fancy R's are suppose to be the set of Reals by the way.. not good with this typing math stuff) Homework Equations The Attempt at a Solution I'm not actually sure I...
  50. S

    Calculating Newton's Gravitational Constant in Different Units

    Homework Statement Is there any standard method known to work with units in which speed of light (c), Planck's constant (h), Boltzmann constant (kb) are given by: c=1 h=2*pi (i.e. h_cross=1) kb=1 For example, how can we calculate Newton's Gravitational Constant (G) in these units. If...
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