What is Units: Definition and 996 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. L

    What Units Should I Use to Calculate Planetary Orbit Time?

    Hi all, I'm working on a problem where I have to find the time it takes for a planet to form from a protoplanetary disk, using the equation: t = \frac {3}{A}M^{1/3} Where A= ( \frac {(1+2\beta)\sigma}{P}) (\frac {3\pi^2}{4\rho_m})^{2/3} However, I'm not sure which units the...
  2. J

    SI units for Heat transfer equation

    Homework Statement I am trying to get the units to match up on both sides. \frac{\partial T}{\partial t} = \frac{\nabla ^{2} T}{k} = \frac{1}{K}(\frac{\partial ^2 T}{\partial x^2} + \frac{\partial ^2 T}{\partial y^2} + \frac{\partial ^2 T}{\partial z^2}}), where k is the thermal resistivity...
  3. R

    Do Scattering Amplitudes Have Dimensions?

    Whenever I see the amplitude for fermion scattering, it comes out dimensionless. However, for scalar scattering, the dimensions are 1/energy^2. For example, for 2 particles scattering into 2 particles in a \phi^3 interaction, there is just one internal line, so the amplitude is proportional to...
  4. M

    Find the value of L. Answer in units of

    Homework Statement A series RLC circuit has a resonance fre- quency of 1360/ Hz. When it is operating at a frequency of ! > !0, XL = 9.7 and XC = 9.3 . Find the value of L. Answer in units of mH. Homework Equations X(L)=w*L The Attempt at a Solution what i did is...
  5. C

    Solar power AC units, soon or never?

    It seems to me that solar power and air conditioning are made for each other. As of now there are several different companies making smaller adsorption/absorption AC units, but they are overpriced compared to their electric driven counterparts giving limited return on investment. Here's what...
  6. Phrak

    Tesnsors and Units Consistancy

    Tensors and Units Consistency Where do the unit labels go on tensors? This discussion is continued from this thread https://www.physicsforums.com/showthread.php?t=321298" Greg, I've been trying to make sense of things in mixed units. Taking the dot product as you've done is a good test...
  7. K

    Force & Volume Fundamental Units

    What are the fundamental base units for Force and Volume? I think its cm3 for volume but not completely sure.
  8. R

    How do vectors relate to the area and length of a rectangle in vector calculus?

    I've been reading a bit on vector calculus trying to get a solid grasp on it. I am wondering how it can be stated that given C=AXB (all vectors), that C is equivalent to the area of the rectangle formed by A and B in the A,B plane. How can you equate length and area. One is in say...mm and the...
  9. A

    Finding the units of the ring Z[sqrt(-3)]

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  10. P

    Modern Algebra - units and zero divisors

    This is my first assignment in my Modern (Abstract) Algebra class, just to give an idea where I am with tools that I can use. Homework Statement Describe all units and zero divisors in Z[i] Homework Equations The Attempt at a Solution I already know the answers are units = 1...
  11. K

    Units Systems, Dimensions & Dimensional Analysis Overview

    I'm searching for an online text on units, units systems, dimensions, dimensional analysis and so forth. A nice overview or summary, or an introduction not geared to the complete beginner. Has anybody a good link? thank you
  12. F

    Work done by a heat engine - quick issue with units used in the solution

    Homework Statement "A gas storage system contains oxygen at a pressure of 5 atmospheres at 300 K. (Here, you may assume that oxygen behaves as an ideal gas.) The volume of the cylinder is initially 150 L. (State 1.) In a fire the gas is initially heated by 200 K, with a safety system keeping...
  13. E

    Units for Einstein coefficients in stimulated emission?

    Homework Statement Hi, I need to know the correct SI units for Einstein Coefficients (A and B) for stimulated emission (say laser). The equation I'm on about is Homework Equations \frac{A}{B} = \frac{8\pi h\nu^{3}}{c^{3}}The Attempt at a Solution after some scribbling I got to \frac{A}{B}...
  14. M

    Units of C & K in d=ω C √(l/g) sin(ω K √(l/g))

    Homework Statement A quantity, d, depends on the angular frequency in the following manner: d=ω C √(l/g) sin(ω K √(l/g)) Determine the units of C and K Homework Equations d=m ω= sec-1 l=m g=m/s2 I substituted this into the equation m=s^(-1) C √(m/(m/s^2 )) sin(s^(-1) K √(m/(m/s^2 )) )...
  15. S

    How Do Radiance Units and F-Number Relate in Optics?

    While reading a paper on optics, I came across "the radiance of the projector is 20 mW/cm2, expanding out onto an f/18 cone." What does the "expand out onto an f/18 cone" part mean? I thought that radiance is just in units of power/area/steradians. What does f-number have to do with anything?
  16. J

    What is the Force Constant for Gaseous 14N16O?

    Homework Statement The fundamental vibrational frequency of gaseous 14N16O is 1904 cm-1. a. Calculate the force constant, using the simple harmonic oscillator model Homework Equations K=u((2pi)(v))^2 u=reduced mass The Attempt at a Solution u=[(14)(16)/(30)] (1kg/6.02e^26)=...
  17. P

    What are the common conversion factors for American Engineering units?

    Not quite sure if this is the correct place to post this, but I am having difficulty converting between AE and SI units. Having grown up using only SI units, the AE units are a little confusing. What is the conversion formula for degrees Fahrenheit to degrees Celsius incorporating a degree...
  18. S

    Half-Life, Nuclear Decay Related Problem (answer in units of Ci)

    Homework Statement The half-life of an isotope of phosphorus is 14 days. If sample contains 2.9 × 10^16 decays such nuclei, determine its activity. Answer in units of Ci. Homework Equations / The Attempt at a Solution I know that one Ci is equal to 3.7*10^10 bq (or decay per second), I'm...
  19. F

    Converting Units: cm^3s^-1 to L/s

    Homework Statement I need to convert a value in cm^3s^-1 to litres per second. I know that 1 litre=10^-3m^3 Homework Equations The Attempt at a Solution Could someone please help?
  20. S

    Packed Absorption Column - Solving for min water rate and transfer units.

    Having much difficulty with the problem below. Any direction would be greatly appreciated. A waste gas stream contains .045 mole of ammonia per mole of carrier gas. Its desired to design an absorber using water which will reduce the ammonia concentration in the exit gas from the absorber to a...
  21. fluidistic

    Calorimeter and heat, units question

    Homework Statement I have a lab report due next week and I'm almost done with it. However I'm totally stuck on the last part where it is wrote in a description of the experience : c=\frac{(m+M_e)(T_f'-T'_i)}{m(T_c-T_f)} where c is the specific heat of a metal. If I work out the units in the...
  22. M

    The Klein-Gorden Equation and the Mass-Sqaured Factor -a question on natural units

    Homework Statement A Consistency question regarding the dimensions of the KG Equation. Homework Equations M^2=\frac{\hbar c}{G} for a quantization of gravitational charge on matter The Attempt at a Solution I know a few things however concerning the KG equation. It is directly...
  23. N

    Dimensional Analysis and units of voltage

    Homework Statement The first equation below has units of voltage. Homework Equations V(t)=IR(1-e^{t/RC}) \rightarrow ln|IR - V(t)| = ln|IR|-t/RC The Attempt at a Solution the logarithm has units of voltage, but what does ln|IR| and ln|V| physically mean?
  24. R

    Torque Units: Help Understanding kg force cm

    Dear Physics Gurus, o:) I am trying very hard to understanding the units used to measure torque. I know there is a unit called kilogram force centimeter, and 1 ounce force inch = 0.072007790632 kg force cm. My problem is I do not understand what these units mean. I could only find...
  25. O

    Deriving Multiplication Factor for Geometrized Units: Help Needed!

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  26. S

    Gravitomangetic B-field units

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  27. J

    Spring problem in British units

    Homework Statement ok this might be a stupid question but I am working on a problem with springs and velocity and whatnot. anyways the units are american, 5lb, k=2lb/in, the diagram is dimensioned in inches. do i have to convert all them to N,kg,and meters. Homework Equations...
  28. Redbelly98

    Wrong units conversion in press

    It really annoys me when professionals mess up unit conversions. From http://news.yahoo.com/s/afp/20090403/sc_afp/usclimatewarming_20090403144320 (1 million km^2 is actually 390,000 square miles.)
  29. J

    Solving Problem with Units: Max Elastic Potential Energy

    Homework Statement In a problem to determine the maximum elastic potential energy of a molecule, I have the following equation: A= \sqrt{\frac{6.626*10^-34 Js}{2\pi}}\times(\frac{1}{(1.14*10^-26kg)(1.85*10^3N/m})^(1/4) Homework Equations The Attempt at a Solution The answer is...
  30. Y

    What is the Conversion for Units in Particle Physics?

    Hello! I was wondering if someone could help me with a problem of units! I'm currently deriving probability equations for neutrino oscillations and I'm stuck with units! I have: [(mass)^2 * time]/[4*energy] and I want to write it as [1.27 * (mass)^2 * distance]/[Energy] with distance in...
  31. T

    Calculate Savings with VFD on MUA Units

    Im am trying to figureout how to calculate savings using a VFD - Variable Frequincy(Speed) Drive Direct energy savings easy I am trying to Calculate the savings in AIR FLOW/+/Air temp-differerance Not exausting 75'F air outside at say 10,000 CFM - And not bringing in 30'F Air in the...
  32. B

    Are Natural Units Truly Dimensionless?

    This is perhaps a stupid question but: When we use natural units and set h=c=1, do we choose appropriate units so that their value is one but these constants still have dimensions, or are we somehow choosing h=c=1 to be a pure number with no dimensions?
  33. M

    Finding the Inverse of a Number in a Finite Field

    Homework Statement Suppose that m = 1 mod b. What integer between 1 and m-1 is equal to b^(-1) mod m? The Attempt at a Solution m = 1 mod b means that: m = kb + 1 for some integer k Let x be the inverse of b mod m, note: x exists since b and m must be coprime due to the previous...
  34. C

    Magnetic Energy formulas, units, and examples

    1. My teacher has given me a poster board to do on magnetic energy even though she has explained nothing about the subject, nor is there anything in my book. I am looking for the formula for finding magnetic energy and examples from everyday life. All I got was 1/2BH, but I have no idea what...
  35. K

    2 problems conserning magnetic fields and units.

    Homework Statement http://www.aijaa.com/img/b/00125/3627010.jpg http://www.aijaa.com/img/b/00758/3627011.jpg Homework Equations E_k=\frac{1}{2}mv^2 \vec{F}=m\frac{\vec{v}^2}{r} \vec{F}=q\vec{v} \times \vec{B} \frac{v}{r}=\frac{2\pi}{T}=\omega The Attempt at a Solution The...
  36. P

    Units of length and time in MeV?

    How do you convert a length which has been given in MeV ^-1 to SI units? Energy is mass length^2/time^2 so I guess it;s easy to make the steps of energy - mass - momentum etc... What about length and time? Cheers
  37. R

    Magnetic Field in Natural Units: Expressing \hbar

    Dear PF members, In terms of natural units the reduced Planck's constant (\hbar) is 1 ML2T-1. Now in this terminology how a magnetic field can be expressed? thanks for your reply, rajini
  38. A

    Ideal Gas Law: Solving for V with Constant R: Units L or m3?

    When using the ideal gas law equation and solving for V, with constant R = 8.314 J·mol−1·K−1, what are the resultant units? L or m3? I always remember it being in L, but wouldn't it be m3 based purely on the units being put into the equation? Other units I'm using: P: Pa (not kPa) T: K
  39. scupydog

    What units is E=MC measured in?

    Hi all could anyone tell me what units are used in the equation E=MC. Thx, Dave.
  40. D

    Is the Answer in Meters per Second or Millimeters per Second?

    Units -- is this m/s or mm/s? Homework Statement N/AHomework Equations Continuity A1*v1=A2*v2 A=pi*r² The Attempt at a Solution I've solved a problem as follows (pi * 10.0mm²)(0.200m/s)=(pi * 2.50mm²)(v2) 3.20 xx/s = v2 I am pretty sure it's in m/s, but having the radii in millimeters is...
  41. G

    Help understanding the units in Gauss's law

    Homework Statement Well, here's the homework question: A charge Q is located inside a rectangular box. The electric flux through each of the six surfaces of the box is: phi1=+1500Nm^2/C, phi2=+2200Nm^2/C, phi3=+4600Nm^2/C, phi4=-1800Nm^2/C, phi5=-3500Nm^2/C, and phi6=-3400Nm^2/C. What is...
  42. P

    What are the units of the radial wavefunction in my FORTRAN code?

    I am solving the Hydrogen wavefunction using FORTRAN. Now using the Euler method, I am given a solution to match which is given by u10(r) = 1.06r*exp(-3.74r) (where unl(r) = rRnl(r) in general) which says it has a normalisation chosen to match what i should get from my code. Then I use the...
  43. C

    Reading a multimeter - units

    I am trying to make sure that the data I read off my multimeter has the right units. I have a multimeter that is a similar model to this one: http://www.tequipment.net/BK2703B.html You can enlarge the image to see the settings. When I measure AC current, my result says "2.95" when the...
  44. K

    Convert Units for Thermodynamics Calculations?

    I am reading something about thermodynamics and everything are not given in SI units. In the material, they use Fahrenheit for temperature, BTU for heat, lb for mass and in^2 for area. Now I need to calculate something with the data given in those units, well, I need to apply equation for ideal...
  45. M

    Proving Uniqueness of Products in Finite Rings

    Homework Statement Let q be the number of units in finite ring R. Show that for all a in R, if a is a unit in R then a^q = 1. Is there a way to solve this without using group theory? All I can seem to find information on is when a and m are relatively prime then a^{\phi (m)} = 1 (mod \, m)...
  46. N

    Matter Defined: Mass, Volume & Time? Unit Ideas?

    The definition of matter is "anything that has mass and volume". Why doesn't the definition of matter mention anything about "time". Should time be mentioned as well since matter can't exist without it? Also, If matter had its own SI unit, what would it be? Edit:: a unit that could be...
  47. A

    Do Friction Forces Have Units?

    Homework Statement Does Friction have units? Homework Equations U = Ff / Fn The Attempt at a Solution I know the coefficient which is "Mew" U, has no units whatsoever but I just wanted to know if friction itself had units.
  48. P

    What Are the Correct Units for p in the Equation R=pl/A?

    Homework Statement rearrange to make p the subject then work out the units for p R - resistance or wire A - area in m2 l - length Homework Equations R=pl/A The Attempt at a Solution p = AR/l (m2 x m2kgS-3A-2)/m Resistance is ohms which is m2kgS-3A-2 I think...
  49. B

    Change Catia Part Units in Drafting Sheet

    I am trying to display the dimensions of a catia part in the Cat drafting sheet.(start-mechanical design-drafting). I get the dimensions to pop up in mm but I want to change the units. I have scoured menus looking for it and I can't seem to find the option. Any help would be appreciated. thanks.
  50. A

    Proving the Converse: Finite Field with Cyclic Group of Units

    Given a field F, I know that if F is finite, then its group of units F* is cyclic. I'm trying to prove the converse: if F* is cyclic, then F is finite. I have no idea where to start; I've tried a few things and they didn't get me anywhere. I know that if F is infinite and F* is cyclic, then F*...
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