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. 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.
  2. 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*...
  3. T

    What Are the Units of Constants c and Fo in the Equation Fv = Fo * sin(cx)?

    Homework Statement A particle experiences a variable force Fv = Fo * sin (cx) where x is displacement in meters. What units are the constants c and Fo in. Homework Equations The Attempt at a Solution Um ok...how the heck do i figure out what units they're in so i know my final...
  4. M

    Unpacking the Meaning of Specific Heat Capacity in Base Units

    specific heat capacity is measured in joule per gram-kelvin (J g–1 K–1). In base units it is m2 s-2 k-1. Is that meaningless to express specific heat capacity in base units? Is there an explanation? Thanks Nick
  5. R

    Energy levels of hydrogen in atomic units

    [solved] Energy levels of hydrogen in atomic units Homework Statement The effective potential for a hydrogen atom can be thought of as the actual potential plus the centrifugal repulsion, written as: V_{eff} = -\frac{1}{r} + \frac{l (l+1)}{2r^{2}} Remembering that you are working in atomic...
  6. D

    What Do the Units Seconds/Degrees Squared Represent in a Pendulum Lab?

    Homework Statement So I'm wondering what the units seconds/degrees squared represents? The Attempt at a Solution I know the unit of angular acceleration magnitude is degree/second squared. Are these related?
  7. tony873004

    Solving Watts Units: V/m From H/m, m/s, W/m^2

    Help with units The book gives the following forumla E_0 = \sqrt {2\mu _0 c\left\langle S \right\rangle } And when it uses it in an example, the units go from: \sqrt {\left( {{\rm{H/m}}} \right)\left( {{\rm{m/s}}} \right)\left( {{\rm{W/m}}^{\rm{2}} } \right)} to V/m, with no intermediate...
  8. N

    Do Operators Have Units?

    Homework Statement Hi all. The title says it all: Say we have an operator - e.g. the Hamiltonian. Does this have units? I.e. does the Hamiltonian have units of Joules or nothing? Personally I think it is nothing, since it is an operator, but I need confirmation.
  9. A

    First principles to find the atomic units of energy,length and time

    I don't know where to begin lol - i know first principles is where you have a general equation which can be derived to give more specific details about something. I have been told that i need to find appropiate combinations of the four defined atomic units that have the desired dimensions but i...
  10. M

    Natural Log of Units: What Happens to the Units?

    Homework Statement We're doing a lab and we basically had to find ln(Pv), where Pv is vapor pressure of isopropanol. Well, the pressure is initially measured in kPa, but what happens to the units if you take a natural log of that whole thing? For example, if I take ln(5 kPa), do the units...
  11. B

    What Are the Units When e Is Raised to a Power with Mass?

    When e is raised to a power with units of mass what is the units of the resulting solution?
  12. H

    What Does the Ångström Unit Mean in Wavelengths?

    I'm sorry if this is the wrong forum but in a problem I was given wavelength with the unit as an A with a circle above it, can anyone tell me what this means and how I can get it into more familiar terms (meters, for example)?
  13. I

    Small conversion of units question

    Homework Statement I don't really know if this is the right place for this question but, we were doing a physics lab and we were using measuring instruments that measure in inches and asked to collect the data for various parts of the lab. My problem is that we were asked to graph our...
  14. S

    Volume/Volume %, manipulating units

    I am trying to find % acetic acid by volume in vinegar. I have 8*10-4 mol/L of acetic acid in vinegar and 8*10-5 of acetic acid in the dilute sample of vinegar and water. I know that the volume/volume % is equal to the amounts of A divided by the total amounts of A and B. BUT that...
  15. F

    Damn units and surface charge density.

    Ok, the question asks: An electron close to a large, flat sheet of charge is repelled from the sheet with a 2.1×10^−12 {N} force. Q. find the surface charge density on the sheet in C/m^2 What i did was use the formula F = qe with 2.1e-12 for the force and 6.1e-19 for the charge of an...
  16. K

    What Are the Correct Base Units for Electric Field?

    A possible set of units of electric field, E, in terms of base units is: a) kg x m x s^-1 x C^-2 b) kg x m^2 x s^-2 x C^-1 c) kg x m x s^-2 x C^-1 d) C x s^-1 e) N x C^-1 I believe it is E but i wondering if there is somthing I am missing. This is how I came up with that answer E =...
  17. M

    The logic behind the cross product with units

    The cross product equals to the area of the parallelogram defined by the two vectors (at least in R^3). So if working on vectors which units v_1 = (1,2,3)m v_2 = (3,4,5)m it correctly returns the according area. However, if used to get a vector perpendicular to each of the vectors the...
  18. J

    Question on brightness units for LED's

    Hello, I've been thinking over for some time about creating a programmable LED display. I have an EEPROM and microprocessor among other things already, so it's not like I'm buying all the parts. Ideally, this display would be viewable from up to 30-40 feet away so it will have...
  19. O

    Simple units conversion (km/h -> m/s)

    So the problem is: Convert 35 km/h to in m/s. I know that: - 1 km = 10^3 m - 1 h = 60 s So I do: 35 km/h (10^3 m/1 km) (1 h/60 s) = 583 m/s But the answer is 9.7 -- What??
  20. J

    Which 'Units' will I benefit most from in a Physics Masters?

    Which Subjects will benefit me more: -Mechanics (Extensive, sound foundation in mechanics) or -Further Pure Maths (If I take all the units, likewise, I will have a better understanding of mathematics)
  21. J

    Why Do People Use G-Units? Exploring Acceleration Ratios

    Why do people use G-units? Essentially it is a ratio of the acceleration with gravity, why not use force directly? Can anyone enlighten me? Thanks.
  22. N

    Convert 112km/h to ms^2: Step-by-Step Guide

    How do I convert 112km/h/min to ms^2?
  23. B

    Volume of Iron (dealing with the units)

    Homework Statement What is the volume of one mol of iron where iron is 55.8 g/mol and the density of iron is 7.86 x 10^3 kg/m^3 ? Homework Equations p = m/v The Attempt at a Solution I can get the numerical answer (checked back of book), but I'm not sure how my units worked...
  24. B

    Units issue when normalizing momentum space wave function

    Homework Statement Check that a given momentum space wave function is normalized. I've done the integral, but the result is not dimensionless. Here is the wave function: \overline{\phi} = \frac{1}{\pi} ( \frac{2 a_{0}}{\bar{h}})^{3/2} \frac{1}{(1+(a_{0} p / \bar{h})^2)^2} The units of this...
  25. D

    How Much Does 2.9955623e+05 Tonne Weigh?

    Hi, Im a studying designer currently working with an engineering CAD program. I have calcualted the mass of the part using an analysis feature in the program. However, I have very little engineering interlect and cannot completely understand the results. The returned result is...
  26. snoopies622

    Converting Geometrized Units: The Role of G and c in Christoffel Symbols

    I am looking at some Christoffel symbols that are expressed using geometrized units, and the only variables to appear are m,r and theta. If I want to convert these to non-geometrized units, how do I know where to place the G's and c's? Is there a consistent way of doing this sort of thing...
  27. E

    Imperial, metric, U.S. customary units

    Hi to all, where can I find specifications (symbol,abbreviation ...) of all units from the systems above ? Wikipedia is not so good for my problem. I' ve found this : http://www.knowledgedoor.com/1/Library_of_Units_and_Constants/Group_Index/acre-foot_group.htm but there is no information...
  28. C

    Capacitance Problem; somewhat solved, but units are off

    Homework Statement An air-filled spherical capacitor is constructed with inner and outer shell radii of 7.00 and 14.0 cm, respectively. (a) Calculate the capacitance of the device. (b) What potential difference between the spheres results in a charge of 4.00 microC on the capacitor...
  29. M

    Surface brightness profiles: sech^2 fit in mag/arcsec^2 units?

    Hi everybody, I have a very quick question about surface brightness profiles for an edge-on galactic disk. I have surface brightness values (V-band, not that it matters) in units of mag/arcsec^2 as usual, as a function of z, which is the distance from the galactic disk's plane. I'd like to...
  30. S

    Units and prime elements in euclidean rings

    A general question. A unit element is one that has it's multiplicative inverse in the ring. An element p is prime if whenever p=ab then either a or b is a unit element. Can a prime be a unit element? The answer is, i think, no but thus far I've been unable to find a contradiction.
  31. R

    Cosmological Constant in mks units

    Hey folks, I'm writing a pop-sci article for a journal and one of the referees wants me to give the cosmological const in mks units instead of GeV. I just wanted to check with anyone in the know if the following looks correct. First, the accepted value of lambda (order of mag)...
  32. D

    (distance)(speed of light)^2 = speed of time with units

    Sorry, I think I made a thread in the wrong section before. I was wondering if anyone thought time could have a speed? If so, what would be its dimensions? I encountered someone who claimed that (distance)(speed of light)^2 = speed of time with units, that would be m^3/s^2 = speed of time...
  33. manjuvenamma

    Units of Solid Angle: SI, Metric & Imperial Systems

    Homework Statement What are the units of solid angle in other systems ( In SI, it is steradian) Homework Equations The Attempt at a Solution
  34. B

    On torque and work having same units

    In rotational motion , the units for torque, \tau = r \times F , are N \cdot m and for work done by a torque, W = \int_{\theta1}^{\theta2} \tau \cdot d\theta , are Joules. Yet both these quantities are homongenous/ have same SI units. Is it so wrong to quote torques in...
  35. manjuvenamma

    Units & Dimensions: Temperature in a Second

    What will be the dimensions of temperature in a particular second, say the 10th?
  36. F

    How Do You Solve the Gauss Units Relation for a Charged Particle's Trajectory?

    Hi all! Homework Statement The problem is: For a particle with electric charge equal to that of one electron, the trajectory radius R is related to the absolute value of the perpendicular component P_{\bot}of the relativistic moment perpendicular to \textbf{B} from the relation...
  37. F

    Understanding Planck's Units: Exploring Dimensions and Fundamental Forces

    Homework Statement 1. What is the meaning of Planck’s units? Hint: Compare the strength of the 4 fundamental forces. 2. Calculate the Planck’s dimensions as a function of the SI units. 3. What are the dimensions of the human being in terms of Planck dimensions?Homework Equations Plancks's...
  38. F

    I-Beam Sizes: Standard Dimensions in SI Units

    Where can I get a list of standard sizes for I beams? (Preferably in SI units, just to save me time)
  39. D

    What Are the Units of the Fourier Transform's Vertical Axis?

    If i have a signal S(t) (the plot would be voltage vs time) and I take its Fourier transform, what are the units of the vertical axis? The horizontal axis can either be frequency in hertz or in radians, but what about the other axis? I guess generally I plot the magnitude of the transform since...
  40. A

    Units of Computing Power: How Much for a 1cm^3 Cube?

    I often hear about how solving some problem would require a computer "the size of the known universe", or something like that. Is there a "unit" of computing power? How many units of this power would say a 1cm^3 cube of hot gas have? In other words assuming you wanted to simulate the actual...
  41. I

    Calculatin units for theoretical magnetic point charge

    Hi, So, assuming the theoretical existence of a monopole, we would have to alter the maxwell equations to give the magnetic field a divergence, and also to ensure that the divergence of the curl of the electric field is still zero we would have to add a term. The altered divergence of B would...
  42. J

    Understanding the Units in Relativistic Momentum Calculations

    I was working a problem in a Modern Physics book: Find the momentum (in MeV/c) of an electron whose speed is 0.600c. My first approach was: mass of electron = 9.1E-31 kg \sqrt{1 - \frac{(0.600c)^{2}}{c^{2}}} = 0.800 p = \frac{9.1E-31 * 0.600c}{0.800} = 2.04E-22 (ignoring units)...
  43. tony873004

    What are the Units for V in Electric Potential and Volts?

    Sometimes I see V representing Electric Potential. Is this the same as electric potential energy? What are the units for V? Sometimes I see V represent volts. But this just seems weird. V is a unit of V? As an analogy, we use kg is a unit of m (mass). We never use m as a unit for m.
  44. J

    Changing Distance Between Zeroes of Parabola at 10 Units Apart

    Homework Statement Let g(x) = x^2 + 12x + 36, a parabola with one zero at x = -6. The parabola moves downward at a rate of 2 units/sec. How fast is the distance between the zeroes changing when they are 10 units apart? Homework Equations g(x) = x^2 + 12x + 36 The Attempt at a Solution...
  45. M

    Refractive Index Units - What Units are Used to Measure Refractive Index?

    Refractive Index Units - URGENT - Homework Statement Does the Refractive Index of a medium have units. If so what are they? i am needing this for a lab report - so i can quote answers and feel fine that i am not giving any units. I am pretty sure there arent any.
  46. C

    Did Mass Have Different Units During the Scientific Revolution?

    This may be a weird question, but oh well. Way back during the Scientific Revolution it would have been possible to define mass as acceleration divided by force right? Then you'd have F = a/m, and the units for force would be different than they are now.
  47. C

    What Are the Units for Coulombs and Volts in Terms of m, kg, and s?

    Im just curious what the units are for coulombs and volts in m kg and s.
  48. E

    Do you square the units when calculating numerically?

    [SOLVED] squaring units Homework Statement When you calculate numerically something like q^2/4*Pi*Epsilon_0, do you square the units of q i.e. is it (q 1.602 176 487 × 10-19 C)^2 or q^2 1.602 176 487 × 10-19 C ? Homework Equations The Attempt at a Solution
  49. P

    Electric Power: V^2/ohm Has SI Units of Power

    Show the quantity volts squared per ohm (V^2/ohm) has SI units of power. P = V x I where P is the power (watt or W) V is the potential difference (volt or V) I is the current (ampere or A) From Ohm’s law I = V / R where R is the resistance (Ohm or Ω). So...
  50. T

    Quantum sensor and units issue

    "quantum sensor" and units issue I'm working on an wireless sensor network for a commercial greenhouse concerned with energy use and efficiency. Much of the literature regarding photosynthetic active radiation uses watts/square meter, but the client has requested a measurement in...
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