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. C

    Seeming paradox when squaring distance depending on units

    Hello all This is probably simple and I'm overlooking something 1 mile = 5280 feet 10% of a mile is 528 feet 528 feet squared is 278,784 feet which is 52.8 miles squared But 0.1 miles squared is .01 miles squared So depending on if you square it as 0.1 miles, or if you convert...
  2. B

    Looking for a Calculator App with Unit Functionality?

    Does anyone know of any calculator apps that can deal with units? I know I can do it on google search, but I was looking for something more like a calculator. I found this one: http://physyapps.com but it's only for iphone and mac. Thanks, Paul
  3. F

    What are the units for angular velocity in this hydraulic piston mechanism?

    Homework Statement Hello, I am doing a mechanisms homework assignment in which a hydraulic piston moves out and moves a link connected to the piston in an angular fashion. I'm just a bit confused about the units of angular velocity and I feel very foolish asking this. Homework Equations...
  4. A

    What Drives the Creation of Derived Units in Physics?

    1) How and When do you multiply or divide or combine units? 2) Is there an intuitive understanding or experience for every permutation of derived units? example: distance is a natural phenomenon we experience and understand intuitively as space between two points or positions we've denoted...
  5. P

    Understanding Units: Multiply vs Divide

    What does it mean to have units being multiplied rather than divided. For example 1Weber which is equal to 1Vs. Saying 1 Volt second doesn't make much sense to me. I understand if it said for example N/m. In general what does it mean to have the units being multiplied rather than divided?
  6. F

    Which undergrad maths units for post-grad theoretical particle physics

    I'm about to begin my third year of a physics major and I want to do units that will best prepare me for honours and post-grad studies in theoretical particle physics and/or particle cosmology. My core physics units will cover quantum mechanics, classical mechanics, electrodynamics, special...
  7. gfd43tg

    Gravitational constant in english units

    Hello, I am taking a fluid mechanics class right now, so I deal a lot with water flowing through a pipe, and equations involving the density of the fluid. The problem is, that since I'm an engineering major, we use way too many english units. There is something inherent about non-SI units I...
  8. A

    How do you do analysis of units?

    Homework Statement Show the unit analysis of this equation that relates frequency to length (in centimeters) of a pendulum f = 5.1L^{-0.5}Homework Equations f = \frac{1}{2\pi\sqrt{\frac{L}{g}}} ? The Attempt at a Solution I cannot find much info about this online, but I gave it a go: f =...
  9. paulmdrdo1

    MHB Find the Two-Digit Number: Exceeds by 4 and 1 Less Than Twice the Units Digit

    The tens digit of a certain two-digit number exceeds the units digit by 4 and is 1 less than twice the units digit. Find the two-digit number. this is my solution, let $x=$ tens digit, $x-4=$units digit. $x=2(x-4)-1$ then, $x=9$ and $9-4=5$ the number is 59 but when I let...
  10. R

    Question about units, if the units are given in the equation or as

    ... part of the value? first example: v (MHz) = 110 B(nT) E^2 (GeV) could someone confirm that when an equation is like this you simply change E into GeV before squaring it and making the calculation? slightly confused. second example: rest mass of a Pion is stated by Wiki as...
  11. Tclack

    Are Planck Units the Ultimate Limit for Measurements?

    So, the three very small quantities: Planck length Planck mass Planck time Does the physical interpretation actually mean for example that when something moves, the smallest distance it can move is one Planck length, that there's no such thing as moving half a Planck length? And further...
  12. S

    Root Mean Square Speed Units Question

    Homework Statement "At 273 K and 1.00x10^-2 atm, the density of a gas is 1.24x10^-5 g/cm^3. A.) Find the Vrms for the gas molecules B.) Find the molar mass and identify the gas (Choose from H2, He, H20, N2, O2, or CO2)" Homework Equations Vrms = √(3RT/Mm) pV = nRT The Attempt...
  13. T

    How to decide on interests ? And 17 units.

    How to decide on interests...? And 17 units. Hello Physicsforums! Here I am again asking questions. I appreciate it if anyone reads this, if not then this was still good for me to rant/think about things. In the past I have not given much effort toward school and failed out of high school. I...
  14. J

    Curl and divergence of units vectos

    Hellow! I'd like to know what results the curl and divergence of unit vectos bellow: https://www.physicsforums.com/attachment.php?attachmentid=65279&stc=1&d=1388593339 I just know that ∇·x = 0 ∇·y = 0 ∇·z = 0 ∇×x = 0 ∇×y = 0 ∇×z = 0
  15. NotAMethDealer

    Is there a safer and simpler method for separating sodium from table salt?

    Any way to easily extract the sodium out of a unit of table salt. Due to the dangers of Cl2 gas I will use a fume hood. Is there any way to isolate the sodium metal without high temperature electrolysis.
  16. A

    Understanding Natural Units in Physics

    So I have been going through a book on physics-based mathematics. I have seen the author using natural units (h = c = 1) in formulae. Why is this done? Most importantly, doesn't it mess up the true calculation? For example, take e = mc^2. If I set c = 1, it becomes e = m. So if I am given a mass...
  17. B

    Multiplying matrix units and standard basis vectors

    Hello all, I don't have a question on homework specifically, but I need clarification on something I'm reading in the textbook. I will be starting an abstract algebra class in the spring and it's been quite a few years since I've had linear algebra, so I'll be reviewing that material before the...
  18. KiNGGeexD

    Expressing Angular Momentum in Units

    If the units of angular velocity, ω, is expressed in rad/a what then is the units of angular momentum? L=Iω From this I can gather that the units are Kgm^2*rad/s Is this a suitable way to express angular momentum?
  19. R

    High order panel modeling units?

    I have a copy of Pan Air (A502) which is a high-order panel method used for modeling 3D airflow around arbitrary bodies. I've read the manual, but I'm not clear about the units used. As I understand it, the free stream velocity is normalized which implies that all the other geometry is scaled by...
  20. T

    Dividing with Units: An Introduction to Math Problem Solving

    Hi,I have found out,that I have problem to understand basic algebra.Especially dividing with units.I do not understand,just what is unit.For example:We have m^2/m=m.But what doe is it mean m^2/m?Dividing with units is easy.We have just some number,and split it to more pieces.But units is...
  21. T

    Help understanding metric units

    Hi all Firstly this is not a homework question. I just found myself wondering what certain numbers meant while at work and realized that i didnt actually know hence the posting. I was hoping someone could help explain & confirm a couple of things about units. 1) Given the number...
  22. R

    Units of the Thermal de Broglie wavelength?

    1. Units of the Thermal de Broglie wavelength? 2. λ = h / (2*pi*mkT)^(.5) 3. through dimensional analysis i get S (J / kg)^.5 can you even have .5 of a unit?
  23. T

    Dimensional analysis, conversion of units in an equation

    We are asked to transform this equation: h=1147(1+0.05625T)\frac{V^{0.6}}{D^{0.4}} where the units of each variable h, T, V and D are: h->\frac{kcal}{h·m^{2}·ºC} T->ºC V->\frac{m}{s} D->cm into another equation where the units of each variable h, T, V and D now are...
  24. nomadreid

    Units of spacetime in Minkowski metric

    In the equation ds2=dx2+dy2+dz2-c2*dt2 the units on the RHS are units of distance squared. But it would seem that units for a spacetime metric should somehow be in units which incorporate both space and time units. Undoubtedly this is an elementary question, but one has to start somewhere...
  25. F

    Convert Units: q,C from gr/lb, gr/gal to mg/g, mg/dm^3

    Hey guys I am having a big problem with this question :frown: Homework Statement The adsorbtion isotherm for the removal of a contaminant from waste water is givern by the langmuir equation: q=(bkC)/(1+bC) where q is the loading of contaminant of the adsorbent and C is the concentration...
  26. MacLaddy

    Help with English units. Specific Heat

    Homework Statement I have a problem that I've mostly solved using Ideal-gas specific heats for Oxygen. It has the form C_p = a + bT + cT^2 + dT^3 I am supposed to give the answer in English units of \frac{Btu}{lbm}, but I am having some difficulties in my conversion. Homework...
  27. A

    What are my units when finding % diff. In kinetic energy?

    What are my units when finding % diff. In kinetic energy? Homework Statement Phrank (36.4kg) runs at 2.2 m/s and jumps onto a large stationary skateboard (2.3kg) on which Phrancine (22.7kg) is sitting. After the collision, Phrank, Phrancine, and the skateboard move at 1.3 m/s. Find the...
  28. Sudharaka

    MHB Understanding Matrix Units for Linear Transformations in M2(Re)

    Hi everyone, :) We are given the following question. I don't expect a full answer to this question, but I don't have any clue as to what is a Matrix Unit. Do any of you people know what is a matrix unit?
  29. N

    Help with spring constant units

    Homework Statement Part 1 (static method): We measured the displacement of a spring (in cm) after adding and subtracting masses (in g). The spring was placed in a vertical position. I am supposed to find the spring constant ks. Part 2 (dynamic method): We did something similar to the...
  30. P

    Relation between units of attenuation

    Homework Statement It is customary to express fibre loss in units of dB/km: \alpha(dB/km) = \frac{10log(P_{in}/P_{out})}{L(km)} where P_{in} is the power entering the fibre and P_{out} is the power leaving the fibre. Show that \alpha(dB/km) = 4343\alpha(m^{-1}) The Attempt at a Solution...
  31. F

    Fluid pressure question in US units

    Homework Statement The ocean liner Titanic lies under 12500 feet of water at the bottom of the Atlantic Ocean. (The density of water is 62.4 lb/ft{}^3.) What is the water pressure at the Titanic? (Give your answer in both pounds per square foot and pounds per square inch.) Homework...
  32. K

    Question about the units of acceleration?

    The general unit if acceleration is meter per second per second. Let's play with the unit of the standard acceleration due to gravity which is 9.8 meter per second per second. Thus how acceleration can be explained if its unit is expressed as 4.9 meter per half second per second or 588...
  33. D

    Solving for Phasor to Complex Units in a Circuit: V21, V13, V34, V24 Calculation

    Homework Statement Several of the voltages associated with a certain circuit are given by V12=9∠30° V, V32=3∠132° V, V14=2∠10° V. Determine V21, V13, V34, and V24. Homework Equations The Attempt at a Solution I am just using this problem as an example as I have no idea how to go...
  34. R

    Solve Energy Homework: Understand (2) & (3) of 1 J = 1 N m

    Homework Statement I cannot understand what is written in my textbook. Homework Equations i.e: 1 J = 1 N m (I get that) ........(1) = 1 Kg m s-2 x m ......(2) = 1 Kg m2 s-2...(3)The Attempt at a Solution If I push a 1 Kg mass (in space) at an acceleration of 9.8 m s-2) then...
  35. M

    Do physics equations work in non-SI units?

    So, will F=ma work if mass is in pounds mass and acceleration in ft/s^2, or will a proportionality constant need to be introduced to the equation? The same question applies to most if not all physics equations
  36. F

    Having problems understanding units

    Sad, right? Problems in Chapter 1! I can usually calculate the correct values, but understanding what the units attached means, I just don't understand the concept...I can't visualize it. For example, For example, in scientific notation the universal gravitation constant G is this according...
  37. B

    Weight vs Mass On Moon and Mars Imperial Units

    Homework Statement Moon's gravity is 5.31ft/sec^2 An object has the weight of 3.5 lb-f on the moon. What is its lb-m What is the lb-m and lb-f on Mars with gravity of 12.1 ft/sec^2. Homework Equations w=mg=mg/gc gc= gravitational constant----> 32lbm*ft/sec^2 for earth The...
  38. J

    Why Does the Cosmological Constant Have Different Units?

    The cosmological constant (Ʌ ) is equated to dark energy and has units of energy/volume. Why have I read that Ʌ equals the Hubble constant squared (H2) which has units of 1/sec2? There must be an obvious explanation.
  39. W

    Grouping all of the units at the end? I.E. F=ma = 2.3*424.3 [kg*m/s]

    In some papers I've read, I've seen the authors write down all of the units at the end. For example ##F=ma = 2.3*424.3 [kg*m/s^2]## In high school, I've never seen the teachers or textbooks write like this. How common is this is method? Assuming one keeps track of their units properly, I...
  40. R

    Converting Units for Thermal Conductivity: A Scientist's Guide

    Dear reader, I thought I was getting the hang of converting units but came across a thermal conductivity value and the unit was given in: BTU/hr-ft-R :eek: I assume the 'R' means 'Rankine'. I want to convert to the SI unit for Thermal Conductivity: W/(m·K) Any ideas? Or if you know where to...
  41. K

    Coupling constants, units and measurements

    I was thinking about units and started wondering about coupling constants. In unit-independent form, the fine-structure constant is defined as \alpha = \frac{k_e e^2}{\hbar c} I don't have a deep knowledge of particle physics but I know that there are weak and strong charges which enter the...
  42. BitWiz

    Do Frames Affect Dimensional Units?

    Say a ship is coasting in space at an arbitrary speed and velocity with respect to an observer. If a joule of energy (generated on the ship) is used to instantaneously accelerate the ship: From an external observer, the acceleration and delta-v observed is dependent on the ship's initial...
  43. Z

    Calculating the Dielectric Function of metals - Units trouble

    Hello everyone here! See i got my hands on this paper: Optical properties of metallic films for vertical-cavity optoelectronic devices by Rakic et al. A simple google search of the title will give you access to the paper. Now, i am writing the function in MATLAB to calculate the...
  44. F

    What known equations have units s²/m² ?

    I invented a weird equation using a substitution that ends up with units of s²/m². I have an idea of what I'm looking and what the value implies but I could use examples of other know equations that use s²/m².
  45. W

    How To Approach Units and Problem Solving Questions?

    Hey everyone, I'm starting to learn physics on my own and I'm doing the chapter review questions at the end of the chapter. Right now, I'm on units and problem solving. My question to you guys is should I be concerned about actually knowing the exact measurement to solve the problems, or is...
  46. F

    How to understands natural units

    I am reading a textbook on special relativity and the author says at one point that he switches to natural units where c=1. The way he quickly explains this is by arguing that if c=3 x 10^8 m/s then we are working in units where seconds = 3 x 10^8m . . . . This has always baffled me and I never...
  47. M

    Homeowners Want to Limit EMF Exposure by AC Units

    Hi, I work in the construction industry. I have a homeowner that would like to protect herself from electromagentic field (EMF) exposure. (She fears cancer from EMF's.) The airconditioning unit in their AC room produces a large electromagnetic field. She wants to prevent this field from...
  48. anemone

    MHB Find the Units Digit of An Expression

    What is the units digit of \left\lfloor \frac{10^{20000}}{10^{100}+3} \right\rfloor?
  49. T

    Is 19 Semester Units Too Much for a First-Year College Student?

    Hello there, I am a first year community college student and I currently have a schedule that is 19 units (the max allowed here unless you want to petition for more). I have no idea if it will be doable for me, as I am new to the college scene and I did not have good study habits in high school...
  50. L

    Question regarding y-axis units in FFT

    Hi all, Havent turned to this forum in quite some time but hoping you might be able to explain to me my y-axis in the audio FFT I have below. How should I understand the units of dB/20u Pa? Ideally I want to convert this into dBa or something, I'm just not sure how to get a "feel" for this...
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