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. M

    Riddle question max profit + units

    riddle question " max profit + units " Homework Statement There is no demand for a new brand of mobile phones if the price is 20 $ or more. For each drop of 1 $ in the price, the demand increases by 500 units.The cost of producing x units is (12x + 2000)$. How many phones should be produced...
  2. J

    Exploring Units in Z(\sqrt{}5i)

    Homework Statement In the ring Z(\sqrt{}5i) = n + m\sqrt{}5i, n and m integers, find the units. Homework Equations -- The Attempt at a Solution I know 1 and -1 are units, and my textbook seems to indicate that \sqrt{}5i and -\sqrt{}5i are also units, but I don't know if that's...
  3. J

    What Are the Correct Units for Density in the Equation P = Patm + ϱgh?

    Homework Statement I'm dealing with densities of liquids. When using the formula P = Patm + ϱgh, where ϱ is the density of the liquid, what should the units of ϱ be? Homework Equations The Attempt at a Solution I have P in kPa, so just looking at the units gives: kPa = kPa +...
  4. D

    Tunnel ionization rates; question on atomic units

    Homework Statement First of all, this is my first post here, so I apologize if I format things incorrectly. I'm working on a Matlab script to evaluate the tunnel ionization rates via the PPT model given the correct set of input parameters. The rate equation I am using contains equations...
  5. L

    How to carry units in integration

    Homework Statement I am trying to integrate from 0 to 10 ft -4x^2/2+4x. I am solving for deflection. The forces are in kips. Somehow the book ends up with k-ft^3. I don't understand how I would carry units in an integration. Any help please? Homework Equations The Attempt at a...
  6. M

    Which of the following are units of momentum?

    A Typo? Homework Statement The question is: Which of the following are units of momentum? The possible answers are: A. N x m B. kg x s/m C. kg x m^2/s D. J x s/m E. kg x m^2/s^2 Homework Equations The Attempt at a Solution Is there a typo on this homework question? I thought...
  7. C

    Unit Conversions: 5000+ Units & 70000+ Conversions!

    Hello everybody! I found a great resource which helps me a lot solving unit conversions. I could find more than 5000 units and 70000+ unit conversions and a lot of discussions on important unit conversions. Here is the link http://www.converter.pk
  8. Q

    Energy vs Voltage and Sqrt(Voltage): Function of Units

    ok, let's say i am plotting a graph of Energy VS voltage so my units will be Joules VS Volt so my gradient will be Joules per voltage but what if i plot ENergy VS square root of VOltage? will it become Joules VS VOLT1/2 so gradient = Joules per Volt1/2 ? my lecturer once said...
  9. N

    How Do I Integrate Kinematics Problems with Units?

    hello, I'm new to the forums. Can someone help me with integrating kinematics problems? For example velocity= Be^(-rt), where B= 3.00 m/s and r=0.500 s^-1. i don't understand how the integral's unit becomes m (since the integral of velocity is displacement). someone help me! thanks
  10. F

    Finding the units (number theory)

    Homework Statement Prove that the ring R of polynomials with real coefficients (i.e. f(x) = a0 + a1x + ... + anxn, ai real, are elements of R) has only the constant term a0 as the group of units, providing the constant term isn't zero.Homework Equations u is a unit if there exists a v such...
  11. L

    Studying Would you say that 28 hours per week is enough studying time (13 units)

    If a student spends roughly 28 hours per week studying, and has 13 units , would you say that this is enough study time for the average person? With classes that are math, science related. This pertains to a student at a 2 year college? Do you believe it would it be different for a...
  12. T

    Exploring the Dimensions of Physical Units: A Deeper Understanding

    Hi =D I was thinking about the physical units (g, m, s, K, J, A, V, etc). I know we got a thing in physics called dimensional analysis, so you analyse some variable that you know it depends on other variables and the two sides of the "equation" (I mean a equation with the proportional sign...
  13. R

    Converting units for Mass Estimates of Astronomical bodies

    Hello! I'm new so I hope I've posted in the right place One quickie please, if anyone can help me :-) I hope to get my mass estimates in units of h70-1 x 10{blah} Msun However! I have found some values in units of just x10{blah} Msun (*) Where they have used h50 in their calculations...
  14. P

    Are All Units in Z[sqrt(2)] of the Form +/- (1 +/- sqrt(2))^n?

    How would I show that every unit in Z[sqrt(2)] is of the form +/- (1 +/- sqrt(2) )^n ? I can show these are all units, but I can't show every unit is one of these. From some research, I'm aware this is a special case of Dirichlet's Unit Theorem, but that is far above the level I'm working at...
  15. D

    Big dimensionless numbers (in Planks units)

    Recently I found this: Note the number - 15360*pi = 48254... This is a biggest number in Planks units I have ever seen In Planks units, what is the biggest dimensionless you have even seen? Anything bigger than 50'000?
  16. A

    Solving Quantities and Units Homework as an Access Student

    Homework Statement I'm stuck on 3 questions from my assignment as an access student (I never studied science before) First thing is: Explain the term " centre of gravity" and where it is in relation to a metre rule. Second: A metre rule is pivoted at its 10cm mark. A 1N force is...
  17. R

    Lennard Jones- reduced units

    Hi friends, I have a question regarding MD simulation using a LJ potential. If I take the e and sigma parameters in the LJ potential to be that corresponding to argon, and calculate some thermodynamic quantity can I convert the value of that thermodynamic quantity...
  18. B

    Cant get units to work out for Momentum Density

    Excuse the question but I am stuck on this for the past hour. Im studying Zweibach's "A first Course in String Theory". From the Nambu-Goto Action he derives the wave equation which consists of the term \frac{\partial \mathcal{L}}{\partial \dot{X} ^{\mu}} &=...
  19. B

    Silly question about units of Momentum Density from NG Action

    Ok, I am thinking that I should probably move this to the Coursework area. I am not sure how to do that or if I even can... My bad...Excuse the question but I am stuck on this for the past hour. I studying Zweibach's "A first Course in String Theory". From the Nambu-Goto Action he derives the...
  20. T

    Why do the E-field and B-field have different units?

    Note this is more of a coursework theory question then a specific homework question. I am learning about E and B fields and electromagnetic waves. A common EM figure I find is the propagation of a photon where the E and B field propagate through space as seen in the following link...
  21. S

    How to calculate density from specific weight in imperial units

    Homework Statement alright so i have to find the density of a clay unit. I am given a specific weight of the clay as 120 b/ft^3, the gravity constant as 32.17 ft/s^2. i need to find the density of the clay, i have no problem arranging the equation below to solve for density but I am not used...
  22. A

    Programs Coming from engineering to science degree, should I keep my units or not?

    Ok so I have done around 1.5 years of maths, science and engineering classes (12 subjects) and realized I didnt enjoy engineering (my major), so I have now changed from a bachelor of electrical engineering to a bachelor of science. Now I am want to include a maths major in the degree however I...
  23. C

    Converting units in scientific notation to other units.

    I'm having some trouble with a few problems that I'd really appreciate some help with. 1.) The velocity of a space shuttle is 8 x 10^3 meters/seconds I have to convert this to kilometers/hours. I know there are 1000 meters in a kilometer, and 3600 seconds in an hour. Next I have to...
  24. majormuss

    Changing Units From Joules to Mega electron Volts

    Homework Statement I always have problems when changing units form Joule form to Megaelectron Volts and vice versa...whats the easiest way to find them? Homework Equations The Attempt at a Solution I always get confused at the conversion part.
  25. B

    Solving Freefall Problem With Special Attention to Units

    Homework Statement A man was standing on a cliff when he dropped a stone. One second later, he dropped another stone. How long before the distance between the two stone is 10 meters? (Show solutions with special attention to deriving the units.) Use g=10 m/s^2.Homework Equations Let d_1 =...
  26. V

    Show that the units for all 3 terms in bernouliis equation are the same

    Homework Statement bernouliis equaton P + 1/2 Rho v^2 + Rho g h = constant find the units of the three terms on the left hand side & show they are the same and then the units of the constant on the right The Attempt at a Solution all i can think to do here is check the SI units...
  27. M

    Are SI Units Equivalent in Differential Equations?

    Hi all, I would like to know if any of you know about anything the equivalence of SI units for differential equations? For example, for the equation E=mc2 SI units for RHS must equal LHS. I am wondering if this would apply to differential equations? I recently came across a journal paper with...
  28. R

    Units of Scalar Field \phi & Lagrangian Density

    What are the dimensions of a scalar field \phi ? The Lagrangian density is: \mathcal L= \partial_\mu \phi \partial^\mu \phi - m^2 \phi \phi So in order to make all the terms have the same units, you can try either: \mathcal L=\frac{\hbar^2}{c^2} \partial_\mu \phi \partial^\mu \phi -...
  29. Z

    Question about super large number units in hubbles constant

    This is hubbles constant from my source 74.2 ± 3.6 (km/s)/Mpc What does the ± mean?
  30. V

    Understanding Units of dex^-1 in Number Density Measurements

    Hi, I've come across a number density expressed in units of Mpc^-3 dex^-1; I understand the Mpc^-3 but not the dex^-1. I know dex is some kind of log scale with n dex = 10^n but I'm not sure what dex^-1 means and was wondering if anyone could help. Thanks!
  31. I

    Find the number of units of the molecule in the river after n weeks

    Homework Statement A chemical plant produces pesticide that contains a molecule potentially harmful to people if the concentration is too high. The plant flushes out the tanks containing the pesticide once a week, and the discharge flows into the river. The molecule breaks down gradually in...
  32. T

    What Does "sr" Stand For in Cosmic Ray Flux Units?

    the unit of cosmic ray flux is expressed as flux /(m^2.sr.s.GeV), so what does sr stand for? Thanks.
  33. T

    Fast Fourier Transform Amplitude Units

    Hi there, So I have a multi year time series of of heights in meters that I am working on. If I compute the FFT on the data and then calculate the amplitude as: abs(FFT)/N where N is the number of samples what units do I end up with for the amplitude? Is it still in meters? Cheers
  34. G

    Units of Electron Volts (AMeV)

    Hi, I have been viewing some publications related to space weather and have noticed that in many graphs and in the articles, the units AMeV appear very often. I am wondering what the A is for? My best guess is that means atomic, ie relating energies of ions rather than single electrons...
  35. Z

    What are the units of spring constant K?

    Multiple Choice Question: What are the units of the spring constant K? I. N/m^2 II. kg/s^2 III. J/m^2 Choices: A. I only B. II only C. III only D. I and II E. II and III I cannot find it in my textbook for some reason...
  36. K

    Prove that Euclidean area is in square units

    Where is it proven that the unit of area in Euclidean geometry must be a square with side=1? Or is it an axiom? Why not triangles or circles to represent area?
  37. K

    Units of vickers,brinell and rockwell. .

    hello everyone. a little question...(or mybe two...)... why does vickers and brinell hardness test have the units of stress ? and why does rockwell test has no units at all ? thanks to all !
  38. P

    Exploring the Bhor Theory: Comparing Units of Energy and Angular Momentum

    I was just studying the Bhor theory and found that if we assume energy is quantised in (nh/2pi) then we can say that the angular momentum of electron is mvr=(nh/2pi) , but the units of (nh/2pi) is joules(Kg m2/s2) as it is energy and of mvr is Kg m2/s so how is it possible to equate them?
  39. S

    Gaussian Units: Electric Field

    I am stuck with Gaussian units. If the field in vacuum is E = \frac{Q}{r^2} Is the field in a dielectric E = \frac{Q}{\epsilon_r r^2} , or is it unchanged?
  40. G

    How do I calculate electricity usage in units?

    How can I work out how many units of electricty are consumed in problems such as the following? During one day, a 2.5 kW appliance was used for 8 hours. How many Units of electricity were used? I know that the answer is 20 but I have no idea how that figure is arrived at. Also, in what...
  41. P

    General Question Kinematics Units

    Sorry for asking this dumb question. The units for displacement is m. The units for velocity is m/s. The units for acceleration is m/s^2. When dealing with kinematic problems would it be incorrect to have units such as km, miles, and minutes in the answer? Should they be converted to...
  42. T

    Quick units question on uniform circular acc

    Homework Statement A centripetal-acceleration addict rides in uniform circular motion with period T = 2.3 s and radius r = 2.80 m. At t1 his acceleration is = (6.60 m/s2) + (-2.40 m/s2). At that instant, what are the values of (a)v dot a and (b) r X a ? Homework Equations i know the...
  43. M

    I figured out the slope for a force vs mass graph but does a slope have units?

    Need to know how to figure out the units on a slope ty.
  44. C

    Units for m & b in y=mx+b Equation

    Homework Statement In an equation of the format y=mx + b, where y=(m1-m2)g and x=acceleration (m/s2) ... what are the units for m and b? (I know that m is the slope and b is the y-intercept, but what do they mean?) Thanks :)
  45. X

    What are Some Units I'm Studying in Grade XI Physics?

    I am studying in Grade XI and have started with physics. Its very different from physics in last grade. So here are my questions about few units my tution teacher challenged everyone about. Homework Statement i)What is the name of the unit [Kg][Meter][Second]^{-3} - We may write it as...
  46. X

    Unanswered Questions on Units in Grade XI Physics

    I am studying in Grade XI and have started with physics. Its very different from physics in last grade. So here are my questions about few units my tution teacher challenged everyone about. Homework Statement i)What is the name of the unit [Kg][Meter][Second]^{-3} ii) What is...
  47. G

    How to Convert Moment of Inertia from Slug-ft^2 to N-m^2

    Homework Statement I am asked to convert moment of inertia of a spacecraft from slug-ft^2 to N-m^2. Homework Equations The Attempt at a Solution Is this a trick question? Usually moment of inertia is expressed in kg-m^2 not N-m^2. 1 slug = 1 lbf-s^2/ft --> therefore 1...
  48. A

    Unifying Relativity and Quantum Mechanics: The Challenge of Planck Units

    Are Planck units the same in all frames of reference ? If so, shouldn't the theory of relativity be modified to account for this ? (same as considering the speed of light the same in all reference frames) Because in it's current form, for a large enough velocity, through length contraction we...
  49. V

    Basic Units: Wavelength, Frequency, Speed of Light

    1.What are the basic units for a) wavelenght of light b) frequency of light c) speed of light 2. What is the wavelenght, in meter, of radiation that has a frequency of 5.11x10^11 s^-1
  50. P

    Accelation problem, how do I change units (km/h to m/s)?

    I made a mistake I meant km/h to m/s^2. 1. ThrustSSC, the world's first supersonic car, accelerates from rest to 1000km/h in 16 s. What is its acceleration in m/s? 2.a=v/t = v-v0/t-0 3. I'm not sure how to change units (Professor didn't show me.), so can you please now all the work to the...
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