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. I

    Studying for old units (a-level)

    Okay, so this isn't actually a chemistry or biology homework question as such. I just didn't know where else to ask this question, if somebody could redirect me to the correct place if it's not acceptable to post this in here, that'd be awesome :) So basically, I'm studying A-level...
  2. C

    Op-Amp Output Units With Oscillatory Input Voltage

    Hi all, ME major here that's very confused about the integrating op-amp. It's pretty simple what I am confused about, just unit problems. Suppose you have the following integrating op-amp circuit: Feedback capacitor: 10μF Input Resistance: 10kΩ Input Voltage: 5V[sin(100t)] My...
  3. adjacent

    Newton's Discovery of Mass, Force & G in SI Units

    What did Newton use to determine the mass of an object(During those days) Even the SI unit for mass was established much time later. The SI Unit for force was also established much later. The G in F=GMm/d2 was discovered in Much later. How did Newton knew that a force of 1N would accelerate a...
  4. B

    Units for Strain? | Learn About Strain & Hooke's Law

    Homework Statement Here is a picture of the problem: http://imgur.com/Ldw1fUF Make sure to click on the picture to make it bigger!Homework Equations The strain/hooke's law equations.The Attempt at a Solution I have this for two parts. The second part is the deformation which I got right. I am...
  5. L

    Potential and wave number problem (concerning units)

    Hi everyone I have the following problem: Homework Statement Give is the following potential for a molecule: E_s(R)=E_s(\infty)-\frac {1}{R}+A*exp(-cR) whereas E_s(infinity)=1.49 eV. A and c are constants which I want to calculate. R(equilibrium) is given as 2.36 Angström and the...
  6. B

    Schools Studying Math Units at University Level - Best Progression?

    Hi Everyone, I hope this is the best place to put this topic if not I do apologize! I'm currently pursuing an IT degree in software development and plan on studying a few related mathematical units that I believe would be beneficial to me. In this regards, Discrete maths, Calculus and Linear...
  7. A

    Problem with units when using E=hv

    In case I'm wrong, the formula for energy of a photon is E=hf. Or E=hc/λ, because f=c/λ. Basically the second formula is just in case you don't know frequency so it crams the equation for that into the equation for energy. When I use E=hc/λ the units I get are... kg*m2/s3 What I did was... A...
  8. G

    How to use ballistic coefficient (SI units)?

    Reading in Russian sources I see they use ballistic coefficients such as these: BC = 3.0 kg/m^2 or alternatively BC = 3.0 m^2/kg That's quite different than the usual G1, G7, etc. Given a certain muzzle velocity, how do I use that to calculate velocity at some point downrange?
  9. M

    Confusing Units after using Bernoulli's Equation

    So in a spacecraft with regular air at 1 atm pressure, a hole gets punched in it (depressurizing it). I'm looking for the Exit Velocity of the air at t=0. Using Units: Internal Pressure: Pi = 1 atm = 101300 [kg / m*s2] Air Density: \rho = 1.2 [kg / m3] And Equation: Pi = 0.5 * \rho * (Ve2)...
  10. L

    Two dimensional discrete Fourier transform units

    Homework Statement I have am doing a two dimensional discrete Fourier transform on an image (using MATLAB). What are the units associated with each pixel of the image in the frequency domain? Homework Equations The Attempt at a Solution I thought that the frequency should be...
  11. G

    Units of Flux Density: Electric Field vs Displacement Vector

    While I do understand the use for the displacement vector D = (e0)E + P, I don't quite understand why they label it as "flux density". The units for the displacement vector are C/m^2. The units for electric flux are Vm, so wouldn't electric flux density become Vm/m^2 = V/m which is just equal to...
  12. B

    Do Assumed Modes Need to Be Dimensionless in Vibration Analysis?

    Hi, I am trying to understand the assumed-modes approach to solving vibration problems. For example, the transverse deformation of a cantilever beam is using two assumed modes is given as ζ(x,t) = ψ_{1}(x)q_{1}(t) + ψ_{2}(x)q_{2}(t) ψ_{1}(x) = (x/L)^{2}; ψ_{2}(x) = (x/L)^{3} In this...
  13. A

    If two units have the same dimensions are they always inequivalent?

    If two units have the same dimensions are they always inequivalent? I was thinking, would doing dimensional analysis on units prove they are equivalent or could they have the same units but not be equivalent.
  14. T

    Dimensional Units for Coulomb in SI

    Does anyone know of a dimensional formula for the Coulomb in SI that does not involve amperes as in A*s? I am looking at some equations and the dimensional analysis is leaving me with C (Coulomb unit charge) and left over m, kg, s to various powers. Just curious if anyone has come across some...
  15. C

    How Do Unit Conversion Errors Impact Fuel Calculations for Flight 143?

    Homework Statement Calculate various fuel quantities for Flight 143. The plane already had 7682 L of fuel ob board prior to flight and tanks were to be filled so that a total of 22300 kg were present at takeoff (a) Using the incorrect conversion factor of 1.77 kg/L calculate in kg the...
  16. M

    Units of Transmittance: Defining & Explaining

    I don't get this. Everywhere I look, the units of transmittance of light are dimensionless. I get that it's a ratio of incident to transmitted radiation, t(f) = I(f)/T(f), and these two have the same units. However, light intensity is always properly defined as the power per metre squared...
  17. K

    Seeking: SI derived units with higher base powers.

    Hey guys, I'm currently working on a chemistry setup and we're building some protocols. We decided that every communication on the protocol between two devices will be in SI units. However, for a data descriptor I plan to use 4 bits per standard SI unit. This means that units for variables can...
  18. D

    How Do You Calculate Angular Velocity in a Rotating Rod with a Spring?

    Homework Statement The 8 lb uniform rod AB shown in the figure rotates in the vertical plane about a pin at C. The spring attached to the rod at D has a spring constant of 1.25 lb/in., and its unstretched length is 24in. If the rod is released from rest in the position shown, determine its...
  19. X

    Voltage Vector/Scalar Components, SI Units, Direction and Polarity.

    All, please help me refine, restate, explain, understand, expand, add, remove, answer the below statements/ questions. Thanks in advance. 1.) Voltage is considered a scalar quantity. (J/C in SI Derived Units) which is a magnitude of energy per coulomb...no direction with this example. Some...
  20. C

    The units for current density don't check out

    In my lectures the equation for current density was given as: J=n*q*vd where: n = the number of electrons per unit area q = electron charge vd = drift velocity of electrons If you rewrite this equation as: J=\frac{N}{A}*q*\frac{dr}{dt} where: \frac{N}{A} is the number of electrons per unit...
  21. S

    Understanding atomic mass units (amu) and weight of particles

    I read that a C12 atom has an atomic mass unit of 12 amu's. A C12 atom has 6 protons, 6 neutrons, and 6 electrons. If the mass of a proton is 1.00728 amu, the mass of a neutron is 1.00867 amu, and the mass of an electron is .000549, how can it's total amu be 12...
  22. G

    Conversion units mystery. Am I wrong?

    Homework Statement The potential difference between two points is 140mV. If 280μJ of work are required to move a charge Q from one point to the other, what is Q? Homework Equations Q = W/VThe Attempt at a Solution http://imgur.com/FDaQfb9
  23. I

    Atoms to Formula Units: Calculate Al2O3 Moles

    Homework Statement A sample of aluminum oxide, Al2O3(s), contains 8.29*10^25 total atoms. Calculate the amount in moles of aluminum oxide in the sample. Hint: This is a two-step problem. Calculate the number of formula units first.Homework Equations N=N × N_{A} The Attempt at a Solution...
  24. J

    Bending power - magnet units question

    I am reading a paper where the bending power of a dipole magnet is described as 2 Tm. Is that Tesla*meter? Is bending power actually power i.e. Work/Time? Can someone explain this physical quantity to me, please?
  25. F

    Energy and power production units

    The decision has been made to install a wind farm with 2000MWe of generating capacity. The rest of the question gives the average wind speed (m/s) air density (kg/m^2) turbine efficiency (%) blade length (m) all of which are used to calculate the power production of the turbine, in...
  26. N

    Converting surface brightness units

    Homework Statement Simply want to know how to convert between mag arcsec-2 to solar luminosities per square parsec.Homework Equations (from wiki) The Attempt at a Solution If the surface brightness S (B band) is 27 mag per square arcseconds, then to solve for the brightness in solar...
  27. T

    Wave Function Units: |ψ(x,t)| - Dimensionless?

    |ψ(x,t)|2 is the probability density. Probabilities are dimensionless. What would the SI units of |ψ(x,t)| be, then? Also dimensionless?
  28. M

    Find units of rate constants and write reactions

    Homework Statement Find the units of k1, k2, k3, k4, and k5. Write rate reactions for dA/dt a. A\leftrightarrowB k1 (forward) k2 (backward) b. A + B \rightarrow C k3 (forward) c. A + R \rightarrow 2R k4 (forward) d. A \rightarrow B k5 (forward) Homework Equations...
  29. P

    Gravitational Force Units Question

    I just have a question concerning a previous thread about gravitation. The formula is from post 19 at https://www.physicsforums.com/showthread.php?t=635188&page=2 v= dr/dt a = dv/dt multiply by dv/dt by dr/dr: a = (dr dv)/(dt dr) = v dv/dr This gets you to the first step...
  30. I_am_learning

    Confusion regarding SI base units

    What qualifies for being called a fundamental quantity and having its own fundamental unit? For example length is considered fundamental quantity and it has a unit of meter. But Area isn't considered fundamental. Is it because we know area can be CALCULATED by multiplying the length of the two...
  31. S

    Basic proof of units in a ring with identity.

    Homework Statement Let R be a ring with identity, and a,b are elements in R. If ab is a unit, and neither a nor b is a zero divisor, prove a and b are units. Homework Equations If ab is a unit then (ab)c=1=c(ab) for some c in R. The Attempt at a Solution Assume both a and b are...
  32. E

    Calculate force in english units

    Homework Statement Determine the force necessary to accelerate a mass of 20 lbm at a rate of 60 ft/s^2 vertically upward.Homework Equations How do you properly account for weight? What exactly is pound force? How do you go from pound mass (lbm) to pound force (lbf)? The Attempt at a Solution F...
  33. J

    Natural Units: What is the Conversion Process?

    I'm slightly confused about natural units. Take mass as an example: I can measure something in kg's, but then decide to convert to MeV/c^2, for instance. To do that I would multiply the quantity in kg by 3*10^8 squared and divide by 10^6*1.6*1-^(-19) i.e. the SI values of the constants. If I...
  34. S

    Understanding Planck Units: The Impact of kB in Temperature Definition

    Hello, Planck units are defined here http://en.wikipedia.org/wiki/Planck_units Length, mass and time are defined via G, c and \hbar and do not involve kB; But temperature contains all G, c and \hbar and kB; Perhaps this is okay; just seems "uneven" that kB appears with a zero power in...
  35. E

    How do you calculate pressure using english units?

    Homework Statement The reading on a mercury manometer at 25 degrees Celsius (open to the atmosphere at one end) is 25.62 inches. The local acceleration of gravity is 32.243(ft)(s^2) Atmospheric pressure is 29.86 (in Hg). What is the absolute pressure in psia being measured? The density of...
  36. E

    Informations (System of Units Brazil -> United States)

    Google Translator.: (Portuguese(Brazil) -> English(U.S.A)) Hello, good morning. I live in Brazil (South America). I'm doing research for the course in production engineering. I found that in Brazil, we use the international system of units...
  37. T

    What are the units for magnetic pressure?

    The formula for magnetic pressure is P_{B} = \frac{B^{2}}{2\mu_{0}} Now, the units on the left hand side are clearly Pascals, but the units on the RHS are T^2 H^-1 m. I've been trying and I can't see how to make the units on the RHS equal the units on the LHS. does anyone have any insight?
  38. C

    Keplers laws of motion - quick question on units

    Homework Statement find the radius R3=((T2GM/(4∏2))1/3 The Attempt at a Solution simple enough, my only question is when I plug in T (units: sec) G (units: m/s^2) and M (units: kg) there is nothing to cancel out the kg so my R is not in units of meters...the equation is correct because...
  39. C

    Help figuring out units in a power fit.

    The equation of interest is: A=B*V^n where A has units of W/(m^2*K) W=watt, K=kelvin, m=meter V has units of m/s. B and n are parameters to be determined.I have a set of values that I put into excel to generate a plot. From the plot, I fit a power trendline to it and got the equation to be...
  40. S

    Help: From Ampere to Coulomb in SI units

    Hello, Could someone help me finish this train of thought? This is how we think in SI units: First, just because we like the value of 1 Ampere as it is now, we choose the force between two parallel conductors to be exactly 2×10^{-7}N= const ×\frac{1A×1A}{1m} Then, purely as choice, we decide...
  41. S

    Gaussian vs SI Units: Comparison & Advantages

    Hello, I was reading about a comparison betw. Gaussian and SI units and the author states "The main advantage of Gaussian units is that they make fundamental physical issues and theoretical relations involving electromagnetic phenomena more clear." Would someone know - is the advantage...
  42. P

    Why does viscosity have units of pressure times time?

    Pascal-seconds is a unit of viscosity. Why? I know that viscosity represents the thickness of a fluid, or its ease of flow, but I don't understand why that is represented by these parameters.
  43. C

    How Do Density, Gravity, and Height Equate to Pressure?

    How is (density)(gravity)(height) supposed to equal pressure? density = kg/m^3 gravity = m/s^2 height = m (kg/m^3)(m/s^2)(m) = (kg/m*s^2)
  44. D

    Need help converting units, momentum of quark question

    Homework Statement A proton has a diameter of about 1fm. Estimate the minimum momentum in units of MeV/C of a quark confined in a proton. Homework Equations The Attempt at a Solution I used the uncertainty relation \DeltaP\DeltaX ~ \frac{\hbar}{2} \DeltaP ~ \frac{\hbar}{2 x...
  45. Y

    MHB Maximizing Profit with x Units: A Math Puzzle

    Hello, I need some help with this question, it is not very clear and I find it hard to translate from text to math... Some company has found that x units of it's product can be sold for p$ a unit when x=1000-p. The cost of producing x units in a day is C(X)=3000+20x. A. Found the income...
  46. D

    When is it safe to use eV units and when do we have to convert eV units into kg?

    Homework Statement I have a misunderstanding of when I can safely use eV units in a formula. For example in the formula p = \sqrt{\frac{E^{2} - m^{2}c^{4}}{c^{2}}} I can put the energy and mass in terms of MeV and get an answer with units MeV/C, which makes sense. But then there was this...
  47. C

    Hydrocarbon Units: ppmC vs ppmC3 vs ppmC6

    I am working on a project about pollution emission, but I am not a chemist. I am seeing the units ppmC, ppmC3 and ppmC6 almost everyday, and I have trouble understanding what they stand for. The only definition I get is "Parts per million hydrocarbon concentration expressed as methane (for...
  48. S

    Clearing Up Units Confusion: How to Ensure Consistency for Density and Rotation

    Please can anyone help me?I'm confused here. If I'm following unit of force as Newton, and length as mm; and stress as MPa,then for a consistent system of units (see link below); http://www.dynasupport.com/howtos/general/consistent-units/ what should be the unit for: 1)density 2) rotation
  49. J

    Why mole and kelvin are basic units?

    Mole is just a number. It doesn't really measure anything so why is it a fundamental unit? And with kelvin - it represents the average energy of the atoms/molecules in a compound. Why is it a fundamental unit? Temperature can easily be represented in joules.
  50. G

    TTU Dynamics - Energy Analysis in American Units

    I am having a problem with dynamics this semester. Our professor gives us "FE-like" questions, which are actually more complicated than FE questions. I can get to where I need to apply the kinetic energy equation but my units look really large and I don't know what to do with W' or how I can get...
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