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. D

    A What is the strength of the strong force in N units

    In addition. 1. what is the presure of this force (alternativly wat is the efferctiv area it is acting on?...nucleai corrss section area?).
  2. D

    Courses Can 18 units be manageable and if so what are some tips

    I'm going to be taking 18 units in the fall. Classes are linear algebra, advanced calculus, statistics, and computer programming (c++). I usually work a lot but this time I've been thinking of talking to work and only working short hours on weekends, maybe 4 hours each for friday, saturday, and...
  3. Lunct

    I What are the units for the Heisenberg Uncertainty Principle?

    To my understanding(correct me if I am wrong), one consequence of the Heisenberg Uncertainty Principle is that energy levels can fluctuate by some amount, e, for a short time, t. As long as e x t does not exceed h/4pi (where h= Planck's constant). My quarry is that what are the units for the...
  4. T

    Temperature Conversions: Understanding the Use of Conversion Factors for Rates

    Why is that whenever we convert a temperature, say ##^\circ C## to ##^\circ F##, we use ##T_F = \frac{9}{5}T_C+32##, but whenever it involves a rate, say ##^\circ C/m##, we only multiply by the slope of the previously given formula? I would say it's because of the latter being a rate so...
  5. M

    How can I check units in Ansys Fluent 18 with SpaceClaim?

    I use Ansys Fluent 18 but the lectures I follow use 16. So there are lots of things different. For example I cannot determine where the units are. In the abvoe vid at 0.12 units are being checked. How can I check them in 18the version i.e SpaceClaim. And I cannot hightlight xy plane as did in...
  6. chloeid

    How do I work out units of velocity from light years?

    Homework Statement I'm currently working through the following question: "A spaceship travels from Earth to the vicinity of the star that is measured by astronomers on Earth to be six light-years away. The spaceship and its occupants have a total rest mass of 32 000 kg. Assume that the...
  7. Const@ntine

    B Solving SI Units with ln(n): A High School Puzzler

    I tried with Google but I couldn't find anything, so here goes: When I "use ln on a quantity" (I don't really know how to phrase it in english, as we just have a verb for it), say, I have n = 0.00149 kg/m*s, and I put it into the ln, so now I have ln(0.00149 kg/m*s) what happens to the SI Units...
  8. Mr Davis 97

    Every ring with unity has at least two units

    Homework Statement T/F: Every ring with unity has at least two units Homework EquationsThe Attempt at a Solution I thought that the answer was true, because if a ring ##R## has unity ##1##, then ##1 \cdot 1 = 1## and ##(-1) \cdot (-1) = 1##. Where am I going wrong?
  9. B

    I Hamiltonian for spin-1/2 particle in B-field: units issue

    Take a spin-1/2 particle of mass ##m## and charge ##e## and place it in a magnetic field in the ##z## direction so that ##\mathbf B=B\mathbf e_z##. The corresponding Hamiltonian is $$\hat H=\frac{eB}{mc}\hat S_z.$$ This must have units of joules overall, and since the eigenvalues of ##\hat S_z##...
  10. Bunny-chan

    Understanding Motion Graphs: Converting Units and Interpreting Results

    Homework Statement I'm having some issues with the following exercise: The graph below represents the marking of a vehicle speedometer in funtion of time. Elaborate the corresponding graphs of acceleration and space traveled in function of time. What is the average acceleration of the vehicle...
  11. Vengo

    B The fundamental units in Physics

    I have been in my physics crash course for my entrance exam. I was looking at the chapter "Units and Measurement". I got a doubt in this chapter and I didn't get it cleared by my teacher. So I am posting this in this forum. We have 7 fundamental quantities and other quantities are derived...
  12. Rizwan Yaseen

    Heat capacity equation units

    How we change the units of Heat capacity equation to British engineering system Cp=2. 657*10^4 +42. 37T - 1. 425*10^-2T^2
  13. C

    I Control Moment Gyro - MOI calculation & units of measure

    Hi all, I am not a physics major and have spent some time learning via the university of Google. I would really appreciate a second set of eyes on what I am calculating and tell me if I am correct, or if I have done something wrong along the way. I am trying to calculate MOI and need results...
  14. P

    Torque -- units and transfer thereof

    Have a general question about torque. I have a 102 inch diameter, ring shaped, flywheel that weighs 500 pounds. It is rotating at 25 RPMs. I know that the energy produced is 1304 joules, but you need to know how many Nm that equates to. Second question: this flywheel is placed in a...
  15. M

    B Units for Entropy of Simple Black Holes

    Hello. I recently discovered Gerard 't Hooft's (what a complicated name to type, isn't it?*apostrophe*apostrophe*apostrophe) equation for the entropy of a simple black hole (what is meant by "simple" I have no idea). It is: Where "S" is the entropy of a simple black hole A is the area of the...
  16. S

    A Kelvin Units: Help Understand Optics of Graphene

    Hey! In https://www.researchgate.net/publication/230937856_Optical_properties_of_graphene article (Optical properties of graphene) I found out the frequency is expressed in Kelvins. Could you help me with it - how did the author do this unit transformation? Thanks in advance!
  17. L

    How do I use this equation? Estimating half-life of a decay

    How should I go about using equation 8.18? Link can be found below. In the book, an example is used where Th-220 --> C-12 + Po-208 with a Q value of 32.1 MeV is used, and it is said to yield t1/2 = 2.3x106 but for the life of me I cannot reproduce this result. This is what I did: Going from...
  18. L

    Pressure variation with sound waves equation

    Homework Statement P(average) for a speaker is 10 W. Gamma is 1.4 (ratio of specific heats), molar mass is 28.8 g/mol, air temperature is 50F, and pressure is 1atm. Find Pmax at 100 I have this equation that gives Intensity = (Pmax^2)/(2*Rho*v) where rho is density, and v is speed of sound...
  19. Vitani11

    Why does work have the wrong units?

    Homework Statement A particle of mass m is moving on a frictionless horizontal table and is attached to a massless string that passes through a tiny hole of negligible radius in the table, and I am holding the other end of the string underneath the table. Initially the particle is moving in a...
  20. Math Amateur

    MHB Units in Z_m .... Anderson and Feil, Theorem 8.6 .... ....

    I am reading Anderson and Feil - A First Course in Abstract Algebra. I am currently focused on Ch. 8: Integral Domains and Fields ... I need some help with an aspect of the proof of Theorem 8.6 ... Theorem 8.6 and its proof read as follows: In the above text, Anderson and Feil write the...
  21. Math Amateur

    I Units in Z_m .... Anderson and Feil, Theorem 8.6 .... ....

    I am reading Anderson and Feil - A First Course in Abstract Algebra. I am currently focused on Ch. 8: Integral Domains and Fields ... I need some help with an aspect of the proof of Theorem 8.6 ... Theorem 8.6 and its proof read as follows: In the above text, Anderson and Feil write the...
  22. J

    Elementary question on Electric flux units

    The net flux over a closed surface is: Flux = The surface integral of the field E = charge / permitivity in space (Gauss law) The permitivity in space is: 8.85 10-12 Coulombs2/N m 2 So I understand the units of Flux are: Newton meter2/Coulombs Is this correct? I don't understand why in a...
  23. ReidMerrill

    How is it possible for v/v units to exceed 100%?

    I'm looking through articles for a presentation in college and I ran across the units volume/volume. (V/V) From what I understand v/v is calculated with the formula (vol. solute/total volume). One of the articles has figures with over 100 v/v. How is this possible? Shouldn't it be between 0 and...
  24. resurgance2001

    I What Does the h Subscript 70 to the Power of 3 Mean in Supernova Units?

    Hi This is a really basic question about units. I have been reading a paper about supernova rates and the units are given as: SN rate per yr MPC^3. h_70^3 (10^ -4) Could someone tell me what the h subscript 70 to the power of 3 means? Thanks
  25. R

    How do I convert cubic picometer to cubic centimeter?

    Part of the question says: An unit cell has a cell edge of 288 pm. I got to the part where volume (288 pm)^3 = (288 x 10^-10 cm)^3 I have no idea how that equals 2.39 x 10^-23 cm^3 Only the Bold part ^
  26. Tahira Firdous

    B FPS System: Why 1 Slug = 15.59 kg?

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  27. Z

    What are the units for Ksp and why are they not always included in calculations?

    Homework Statement I have found, through experimentation, the ksp of calcium hydroxide to be 3.0 x10^-7 (which i know has a pretty large percent error). However, i am conflicted as to what the units should be because logically, plugging the units into the ksp equation should give you units of...
  28. B

    Can a Unit Also be Nilpotent? Proving the Contradiction

    Homework Statement First Claim: If ##u \in R## is a unit, then it cannot be nilpotent Second Claim: If ##u \in R## is nilpotent, then it cannot be a unit Homework EquationsThe Attempt at a Solution I realize these are simple problems, but I have no one to verify my work and I want to be...
  29. B

    I Units of Amplitude & Frequency in Coding (n=0 to 52920)

    for (int n = 0; n < 52920; n++){ F = Amplitude * sin(2 *pi*n* Frequency/44100) ; } what are the units of Amplitude ? I know Frequency is in Hz also what are the unit of F?
  30. D

    I Integrating imaginary units and operators

    When integrating terms including the imaginary unit i and operators like position and momentum, do you simply treat these as constants?
  31. P

    Units of the given potential box

    Homework Statement A car (particle) with mass m = 1 t drives into a barrier with a height of 1 m and a thickness of 3 m. The kinetic energy shall be sufficient to get classically over a barrier with half of the height. Derive an equation for the tunnelling probability. What is the probability...
  32. T

    I Exploring the Mystery of 3 Basic Units

    Hello everyone. As far as I know, any unit can be expressed in terms of basic units: time, length and mass. It quite clear that we could choose them differently but in any case we get three units as the base.. And I ask: Why? What fundamental properties of nater make it It happens that any...
  33. P

    B Wave function, units in the argument

    I will be very grateful if someone could explain to me the following, in the most simple terms, f being a wave function : " ...f = f(x–ct). Let me explain the minus sign and the c in the argument. Time and space are interchangeable in the argument, provided we measure time in the ‘right’ units...
  34. E

    B What does the multiplication between two units mean?

    It seems like division between two units is a simple intuitive concept to grasp, such as velocity, for every interval of time, a particle travels a certain distance. However, I've always had trouble trying to find an intuitive sense for multiplication between two units, e.g. what exactly does...
  35. Vitani11

    Units of orbital angular momentum QM?

    Homework Statement A hydrogen atom is in the 3d state. Determine the orbital angular momentum. Homework Equations unnecessary The Attempt at a Solution I already know how to figure this out and have an answer but WHAT ARE the units?! It's not kgm/s^2!
  36. A

    What are the units of Kp, (Gas phase equilibrium)

    I know the units of Kc are mol/liter. The units of Kp are either mol/atm or just atm. Not really sure. I get mles atm and liters in my answer when i solve. Pretty weird
  37. S

    How do the units of polarizability differ between SI and Gaussian systems?

    Can someone explain how it is possible for polarizability to have units of volume? uinduced = αEapplied so when i divide u_induced by E_applied I get units of (C*m)/(V/m) = (C*m2)/(J/C) = (C2m2)/J
  38. Nader AbdlGhani

    I Why Planck's Constant Has Dimensions and a Unit?

    Despite being a constant, It has both dimensions and a unit, can someone kindly explain why ?
  39. N

    Correct formula for induced voltage with a stationary coil?

    I'm making an AC generator with a stationary coil and rotating magnets. What would be the correct formula to find induced voltage at a certain rotation speed (along with the units)? All sources I've found are either non-applicable or do not explain what units to use. Thank you for the help.
  40. Biker

    B Dimensional analysis and units

    Hello, I have been doing high school physics for about 3 years now and I am perfectly fine with it. However, Something tricked me off few days ago. It is how we treat units. I was kind of hesitant to post this thread because I have seen multiple threads about it before and some member really...
  41. S

    Natural units and electron mass

    I am trying to express some physical constants in natural units of ##c=1## and ##\hbar=1##. Let's start with the electron mass. In SI units, the electron mass is ##0.511 \text{MeV}/c^{2}##. I understand that in natural units, the electron mass is simply ##0.511\ \text{MeV}##. Now, is the...
  42. Oannes

    Finding Surface Area in square feet with Volume & Thickness

    Homework Statement How large a surface area in units of square feet will 1 gallon of paint cover if we apply a coat of paint that is 0.1cm thick? Homework Equations Since Volume is L * W * H and we can assume the object is square besides the height which in this case will be the thickness. So...
  43. Stephanus

    B Discrete definitions of Physics Standard Units

    Dear PF Forum, Perhaps it's not a question, just a light discussion. Time From this, we get the standard time https://en.wikipedia.org/wiki/Caesium_standard, it's 9,192,631,770 ticks per second. I think this number should be discreet. No need to tune it to some figures after decimal point. Is...
  44. RabbitWho

    Expressing measurements in SI units

    Homework Statement I am given some measurements and I am supposed to express them as standard SI units. I can't find any examples of this done online or extra practice exercises to help me. I am probably googling the wrong words. I have been out of school for quite a while and I don't know what...
  45. T

    Cooling Calculations: 5 Amp vs. 30 Amp Units

    Homework Statement If a 5 amp unit can cool 4 cups of water from 75 to 50 degrees fahrenheit in one hour, what temperature could a 30 amp unit cool 128 cups of water in the same amount of time? Is there enough information here to get an idea about what the 30 amp unit would do? If so where...
  46. A

    A I have some problems with units, can someone help me?

    Can someone help me to calculate the unit of gamma from the eq. (2.3). From Eq. (2.2) I assume, it must be [s^-1], but I can not produce it. Thanks Amelos
  47. entity314

    What are the units for the hysteresis coefficient in transformer losses?

    I'm working with hysteresis losses in transformers at the moment, and I was wanting to know if there are units for the coefficient. Normally, I'd just rearrange the equation for units, below, h=ηB1.6f η=hf-1B-1.6 so it would have units JsT-1.6 However, given the power of 1.6, I'm not sure it...
  48. C

    B For oscillations, why do we use angles in waves and oscillat

    For example, the term angular frequency, it units is radian per second. For phase, it is also measured in radians or degrees, why is that? Why is the math the same when you use angles to describe oscillations?
  49. R

    Units of sound pressure level, example: 120 dB re 20 μPa

    I am trying to do a calculation using a value of -211dB re uPa/V , are these SI units? i.e. if OCV = -211db re uPa/V and I have RL = 20log(Vrms) - OCV Do I need to convert the OCV to standard units before putting it in the equation? Wiki isn't so clear about this:
  50. Ecthe

    Atomic units of frequency and angular frequency

    To calculate the Keldysh parameter, I need to use the optical frequency of a laser in atomic unit. Since for the time: 1 a.u. = 2.42×10-17 s, I would assume that for the frequency: 1 a.u. = 4.13×1016 s-1 which is juste the inverse of the time one. However, I found several sources such as...
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