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

    Trying to gain proficiency in dimensional analysis- list of common units?

    Is there good list of common units (good as in including the unit, symbol, and quantity it measures) anywhere out there? I did some searching and came up with this, but I'm unsure how good it is as a source. http://www.alcyone.com/max/reference/physics/units.html Any supplementary list or...
  2. D

    Derivatives and Integrals of units

    I couldn't decide whether to place this in the Physics or the Math section of the forums, deep down it is really a Math question for Physics problems. So mods please move if you feel it would be more appropriate in the Physics section. So when doing calculations, I always like to make sure my...
  3. J

    Heat Capacity: Units, Mols & Avogadro's Constant

    I have the equation for heat capacity for constant volume and pressure. Cv = Cp -R So for Cp I have the units J/k and for R the units are J/k mol. So my question is related to that mol. Is it right that I need to get rid of that mol? if so how? Does it involve Avogadro's Constant? Or do...
  4. S

    Units of principal specific heat

    mechanical (work) unit is J/kgK Heat unit is kcal/kgK what is this mechanical (work) unit, Heat unit ? I'm not able to understand it. please elaborate
  5. A

    Do time and space occur in quantum units?

    Hi folks, I've never taken a real quantum physics course, so this question miiight be really silly, but here it is: I'm wondering if there's any research going on or any established theories about time and space themselves occurring in quantum units rather than occurring in a continuum that can...
  6. S

    Answer: Pressure Differentials in Double Glazing Units

    Pressure differentials in Double Glazing Units Hi I hope I'm in the right place. I'm also hoping that this problem will appeal to someone! I'm a joiner and I make windows. I am in a discussion on a woodworking forum about the physics of a double glazed unit and it's starting to go above...
  7. M

    How Do W/m² and kg·s⁻³ Compare in Physics Units?

    Homework Statement trying to show that the units W m-2 are equivalent to kg s-3 Homework Equations 1 W = 1 J s-1 ? The Attempt at a Solution energy per unit time? p.s. I am very new to physics, a beginner in understanding the whole concept of units, any advice?
  8. J

    I'm having a hard time visualising how the units of torque are

    I'm having a hard time visualising how the units of torque are measured. I can picture how quick m/s or RPM is. But when it comes to torque, I cannot picture what 'x' amount of N/m does. Example, for a motor with 3.3 Lb-Inch or 7N/cm. Does it move 3.3lb of weight per inch? Does that mean...
  9. T

    This should be an easy one units in Pressure formula

    Homework Statement A problem about pressure vs. temperature of a gas. Details not necessary since I'm just looking for specific help (see "Relevant equations"). Homework Equations P = 0.0034T + 0.9517 This is the equation that I'm given, which is the slope of the line plotting pressure vs...
  10. K

    What do the units of diffusion coefficient mean?

    I see that the diffusion coefficient (of diffusivity) D has units of something like cm^2 / s. I'm having trouble understanding what those units mean. For example, speed has such units because something travels a certain LENGTH in a certain TIME. Could someone explain this for me? Thank you.
  11. N

    Common derived units of the physical quantities

    Hi all! I came across 2 questions on my course work, and i don't know what is required here, can some one help please? Q.1 Define the common derived units of the following physical quantities; and express them in terms of the base units: Mass, Length, Time and Electric charge (or Electric...
  12. Phrak

    What are the units of vectors and dual vectors?

    What are the units of vectors and dual vectors? And where do the the units in the metric need to be placed so that V^{\mu}V_{\mu} is a scalar? Taking charge density and current density that combine as a 4-vector, J^{\mu} \partial_{\mu}, and it's dual vector J_{\mu} dx^{\mu}, which units go...
  13. T

    Units into Log and Exponential Functions

    Hello, Something I've wondered about for some time is what happens to units once we pump them into a exponential or log function. For example in neutron attenuation I(x) = I_0 * exp(-Sigma * x) I feel like this something I should know, but I just don't get it. I suspect what's...
  14. H

    Calculate Electric Power from Mass, Radius & Velocity: 3000 Joules to Watts

    A mass M is at the top of a rotative arm, with a radius R, at a certain speed V. Lets take M=60kg, R=5meters and V=10m/s. We assume the movement generated from some kind of natural source (wind, water..), is permanent and constant, and there is no loss (100% efficiency). How many watt of...
  15. D

    Mean motion of Halleys Comet (question about units)

    Homework Statement I'm trying to find out the mean motion of Halleys Comet using the equation. n = \sqrt{\frac{GM}{a^3}} where we have taken the mass of Halleys comet to be negligible compared to the sun, M is the mass of the sun and a is the semi major axis. The Attempt at a...
  16. S

    What are the units for the right side of this equation?

    \nabla\times\mathbf{B} = \mu_o\mathbf{J} + \mu_0\epsilon_0\frac{\partial\mathbf{E}}{\partial t} someone tell me what the units are for the right side of this equation? is it T*(m^2)/s ?
  17. A

    Understanding m.k.s. Units for Electric Field

    This was part of a problem found in my book. Not really homework problem so I'll post it here. Electric field on a certain region is (E is a vector of x,y, and z components) (t is a independent variable in meters) what kind of unit is this? I do realize unit of E is N/C or also in...
  18. R

    Conversion of units (tangential velocity)

    This should be very easy but I can't see what I am doing wrong... V_t=\mu .d where vt = tangential speed (in km/s) d = distance (in km) mu(radian/sec) Now by converting I should get V_t=4.74\mu .d vt = tangential speed (in km/s) d = distance (in parsec) mu(arcsec/yr) but...
  19. L

    What are the units for the equation E=gamma*m?

    I'm using the equation: E=gamma*m I want to know what the units of each of the quantities are. If I want to calculate the Lorentz factor, then do I need to make sure that both the Energy and mass have the same units? I am also using the equation for length contraction: L=L0*gamma Do I...
  20. D

    Interpreting Units: km-1 Explained

    Apologies for the newbie question, but when it is written km-1 does that mean (103m)-1 or 103(m-1)? Thanks in advance!
  21. K

    Molecular Weight Units for Mean Square Speed Calculation

    I need to calculate the mean square speed of molecules in an ideal gas. Mean square speed is equal to 3RT/M, where M is the molecular weight. But what units do I use for the molecular weight if I use 0.08206 L.atm/(mol.K) as R? Thanks a lot.
  22. U

    How to Convert CGSEm to SI Units?

    Homework Statement Got a charge of 2CGSEm need to find it in SI Homework Equations 1C=2.998*10^{9}CGSE The Attempt at a Solution Just a plain question, I get q\approx6.66*10^{-10} Is that correct?
  23. K

    Determine the units of the quantity described

    Homework Statement Determine the units of the quantity described by each of the following combinations of units: a. kg (m/s) (1/s) b. (kg/s) (m/s²) c. (kg/s) (m/s)² d. (kg/s) (m/s) Homework Equations n/a The Attempt at a Solution I would attempt to solve the problem, but I...
  24. J

    Simple projectile motion - problem with units

    Homework Statement (a) A ball of mass 0.4 kg, initially at rest, is kicked directly toward a fence from a point 20 m away, as shown below. The velocity of the ball as it leaves the kicker’s foot is 17 m/s at angle of 42◦ above the horizontal. The top of the fence is 5 m high. The ball hits...
  25. W

    How Do You Convert Milliseconds to 8.68 Microsecond Units for RPM Calculations?

    Hi all, I'm running a microcontroller that has me program times in 8.68microsecond units, and I'm having an issue converting 10ms to 8.68us units, then counting a number (scalar) then taking that number and getting RPMs from it. Here's what I have so far: 10ms = 10,000us...
  26. R

    The Ampere in alternative units

    Could the Ampere be given in units such as N.s.m^-1 ? Would this be correct, i originally just thought it would be N.m^-1
  27. M

    Adjusting Our Units: Can Fundamental Constants Have Integer Values?

    Is it possible to adjust the length of the meter, the length of time of a second, the amount of mass in a gram and the other basic SI units in a way such that all the fundamental constants of nature have integer values?
  28. A

    Maximizing Profit: Balancing Cost and Price for 300 Units

    Homework Statement A company can do 300 units per week at a weekly cost per unit of $58 for labor and supplies. If the charge is $100 per unit, then it would have clients for 300 units. However, for each $5 price increase, it could expect to have 10 fewer units. Homework Equations...
  29. N

    "Find Out 1 meV in Å from E1/2 Equation

    Homework Statement Hi I am told that 1 (E)1/2 = 9.045Å-1, where E is the energy in meV. How do I find out what 1 meV is in Å from that? All I can get is the correspondence between meV and Å-2, not meV and Å.
  30. M

    Space-Time curvature? the units?

    What would the units be on the curvature of spacetime? G(curvature)=8πGT/c^4
  31. M

    Question About Conversion Units

    I didn't use the template because I'm trying to understand a concept which applies to many problems rather than just one. Many times in exercises I am assigned, I am asked to convert from one unit of measurement to the other. For the most part it's easy to understand, but what confuses me is...
  32. A

    Can Pulsars Provide More Accurate Time Standards Than Atomic Clocks?

    Time standards are now based on atomic clocks. A promising second standard is based on pulsars, which are rotating neutron stars (highly compact stars consisting only of neutrons). Some rotate at a rate that is highly stable, sending out a radio beacon that sweeps briefly across Earth once with...
  33. C

    KG and SEC as the basis of all units?

    About 6 minutes ago I thought of this, and I want to check if it is true. Is the kilogram and the second a basis for all units in existence? That is, can all units be derived from these two? I can't think of any other units that are independent.
  34. Pengwuino

    Question about Natural Units in High Energy Physics

    I have a quick question about the units used in high energy physics. In natural units, c = h = 1, but I keep seeing time referenced as t=\frac{1}{m^2}. I figure there's 2 h-bars on top but that still leaves s^2. Can someone straighten me out here? Thanks!
  35. M

    Exponents that have units (how to deal with them)

    Homework Statement So I'm going over the simple yearly interest formula A=P(1+r)^t, where 't' is in years, 'P' is in dollars and is the size of the initial investment, 'A' is in dollars and is the total interest earned in a given period of years, and 'r' is the rate at which the investment...
  36. K

    Instantaneous Unit Conversion between CGS and SI units

    In doing some research, I cam across an equation for instantaneous radiated power, with the CGS units "erg/(sec rad cm)", rad being radians (not rad the unit for radiation exposure). Try as I might, I'm not able to come up with a way to convert it to the SI units for watts. Does anyone know...
  37. P

    Units of RC are the same as time - help

    Homework Statement the title says it all, we are required to show that the units of RC are the same as the units of time. ie. iohm * 1 farad = 1 seconds Need help thanks Homework Equations The Attempt at a Solution
  38. L

    MATLAB .Explaining the Y-Axis Units of Spectrum Density Calculated by MATLAB

    Recently we have received a revision of one manuscript. One reviewer request an explanation of the units of the y-axis of the spectrum density (calculated through fft MATLAB algorithm). As we are not physics or mathematic we have troubles to perform an appropriate response. The units that...
  39. B

    Do I always have to convert to SI units?

    Hi, I'm trying to calculate the minimum mass of a star, where M=PV³/2πG The values I've been given are V=400km s^-1 and P=34.4 hours. Does this mean that I have to convert these values to SI units, i.e. give the values in terms of metres and seconds rather than km and hours? This would...
  40. R

    Conversion Formula for Intensity Units: SI to AU Explained

    I know that the SI unit of Intensity is W/m^2. I came across one more unit of intensity -> AU..but could not get much on that. Can anybody tell me the conversion formula ( from SI to AU ) ?
  41. C

    What are the units for centrifugal force and how do you calculate it?

    I found this on Wikipedia for the equation relating to centrifugal force. F = d/dt (m*v) So I have my mass and velocity but I just multiplied the two, that can't be correct can it. You have to derive something I imagine. Also would the units just be in lbs or Newtons. I'm using feet/s...
  42. M

    What units does incident light have in UV spectroscopy

    Hi What units does incident light have in UV spec? Is it joules? Transmission is defined as transmitted light / incident light so any units of light simply cancel out to give a unitless number. I presume the original units were joules as light is EMR? Perhaps its more complicated than that...
  43. R

    Units for wave vector and other?

    Homework Statement Wave vector = k, what's the unit? http://en.wikipedia.org/wiki/Uncertainty_principle#Robertson.E2.80.93Schr.C3.B6dinger_relation" In that equation, what is the name of the h (modifoed h) and what's it's units? Homework Equations k = p/h (not a normal h) The...
  44. C

    Why are English units so confusing?

    A Jigger is three mouthfuls. A hogshead is two barrels. A furlong is "The distance a plow team could be driven without rest." A mile is eight furlongs. A league is "intended to be an hour's walk." I'm not even going to get into the mess that is the definitions for weight...
  45. C

    Derivation of classical limit in c = 1 units (i.e. without cheating)

    So, we start with special relativity in c = 1 units. The equations for energy and momentum can be written as: E = E_{0} \gamma \vec{P} = E_{0} \gamma \vec{v} where E_{0} is the rest energy, \gamma = \frac{1}{\sqrt{1-v^2}} and \vec{v} is the (dimensionless) velocity. We...
  46. D

    Why is h-bar rather than h used in Planck units?

    Learning a bit more about Planck units, it looks like a number of arguably arbitrary, or at least pragmatic, choices had to be made, regarding using G versus 4piG, using 1/4piEpsiolon0 versus Epsilon0, and so on, but in the reading I don't see any question that h/2pi, rather than h, is the best...
  47. B

    Histogram of number of units selected

    I have some things that have a 7% chance of being blue, 10 of these things are put in a box. What is the percent chance that the box will have exactly one blue thing? Two blue things? and so on.. I have simulated this and came up with the following (all appx) 0 - 37% 1 - 37% 2 - 18% 3 -...
  48. N

    LaTeX LaTeX: Tables and Columns and Units, oh my

    I'm trying to make a table in LaTeX in which all the entries of a column have the same units, without having to type them for each column. (Before you say it, yes, I know I could just put the units in the column heading, but I don't want to). I tried: \documentclass{article}...
  49. N

    Units of Square root of a quantity

    Homework Statement Example: If the tension in a string is 25N, the square root of that tension would be 5 ...what?
  50. C

    Can We Take the Derivative of a Unit?

    okay we know that velocity is in meters per second and that acceleration is in m/(s^2) , so if I take the derivative of velocity with respect to time i get acceleration . but just looking at the units , if i start with velocity m/s (ms^-1) this might sound crazy but can i just take...
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