What is Units: Definition and 995 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. jybe

    How Do You Convert and Round Measurements to SI Units with Significant Figures?

    Homework Statement If I am asked to give my answer in acceptable SI units and to 3 significant figures, how would I express my answer? Homework Equations Answer: 589883.4263 J The Attempt at a Solution My instinct would be to put this in KJ, but I don't know if that's an "acceptable SI...
  2. L

    SI Units: Is the combination of SI units still an SI unit?

    Homework Statement Is N/m^2 a si unit I know Newton is and meters but togeather are there or is m^2 Homework Equations The Attempt at a Solution N/m^2 m^2
  3. C

    MHB Understanding Unit Cancellation in Physics Equations

    here's the question: a = b/e b = 1 kg m-1 e = 1 kg m-2 what is a? including units I assume it's to do with cancelling out the units when you divide but I really don't know what the answer is
  4. nomadreid

    Units of capacity for the manufacture of flexo printing plates

    I am not sure that this is the right place to post this question, so I will be happy to let any moderator move it. (I would be less happy to find out that the question has no place in PF, but I would accept it.) I have been asked to make a list of American manufacturers of plates for...
  5. Poetria

    Air Pressure Conversion: Units to Meters

    Homework Statement [/B] dp/dh = -.13*p h in kilometers I should convert it into meters2. The attempt at a solution I thought it would be enough to multiply -0.13 by 1000. :( dp/dh = -130*p but it is wrong.
  6. J

    Understanding Unit Cancellation in Equations: A Guide for Confused Students

    Homework Statement I've an equation here: h = 3270 Pa / 1,0 g/cm^3 × 9,81 m/s^2 = 33 cm How did those units cancel out to make it cm? That's something I don't get. Homework Equations Given above. The Attempt at a Solution I've tried to cancel them out by looking at the same unit in the...
  7. R

    Absorption coefficient units

    Why is the absorption coefficient (##\alpha##) of water is always given using the units ##\text{length}^{-1}##, while for other materials it is often given by ##\text{length}^{2}.\text{mass}^{-1}##? For instance, this paper uses ##cm^{-1}## for water and yet ##cm^2 / \mu g## for other...
  8. opus

    Differentiation with units- Related Rates problem

    Homework Statement A spherical balloon is being filled with air at a constant rate of ##2cm^3/sec##. How fast is the radius increasing when the radius is 3 cm? Homework EquationsThe Attempt at a Solution This is a problem given and spelled out in my text. However, it seems to be assuming that...
  9. I

    I How do I convert mass units in physics?

    I am enrolled in a course related with physics, and we have a table of equivalencies of units to get the right units of frequencies. Stiffness Mass Frequency tonf/m ton.s^2/m rad/s kN/m ton rad/s N/m kg rad/s kgf/m...
  10. G

    I A question about units in equation: Dimensional analysis

    This question is about the matching the unites in an equation. The equation for an electron mobility is given by m^2/V.S. However substituting the units in the equation, doesn't yield the unit of mobility [m^2/V.S]. I have done the simplification using mks units and didn't come up to m^2/V.S...
  11. jamiebean

    Basic physics units problems involving the Ideal Gas Law

    Homework Statement The following is the equation of ideal gas law, where p is pressure (Force/Area), V is volume, n is number of moles and T is temperature in Kelvin. What is the fundamental unit of R? pV = nRT A. kg^−1 · m^−2 · s^ 2 · K · mol B. kg^−1 · m^−4 · s ^2 · K · mol C. kg · m^4 · s...
  12. Q

    I How do we justify "Natural" Units

    How is it that when using "natural" units we drop the units themselves. I understand that you can arbitrarily change the magnitude of a parameter by choosing a new unit. For example Oliver R. Smoot is exactly 1 smoot tall. However, in natural units with [c]=[h/(2π)]=1 the "smoot" part is...
  13. T

    B Measuring Objects using Dissimilar Units

    Quantumly speaking: Can speed be measured? If so, why? If not why? This is a serious question. Speed involves a distance unit and a time unit. For example .. "ft/sec" .. and it is illogical to divide seconds into feet. Having made this point can speed be quantumly measured and how do you...
  14. Arjun Singh

    KiloNewton/Pound foot of thrust into Horsepower units

    Hi, I am currently studying aviation engine outputs and to make my study linear in comparative analysis with standard Automotive engines I need some expert help. Can anyone help me drive precise equations to convert: 1. Engine thrust in Kilo Newton into Horse Power and Watts 2. Engine thrust in...
  15. J

    B When Difference between Kelvin and Celsius are negligible

    This question is more for practicality than anything else, and I realize it may be partly subjective. At what temperatures can the 273 degree difference between Kelvin and Celsius scales be ignored? I'm thinking for examples regarding stars and very high temperatures. Surely once you get to 15...
  16. enter

    Why does America still use imperial units in science?

    America is mostly leading in science, especially in astronomy, yet they still use imperial units. (I am not talking about the great people doing the science.) Everyone else is using SI and the metric system however they insist on using miles, yards, pounds, feet, etc., and continue on being a...
  17. S

    Geometric buckling help needed :) Units?

    Mentor note: Thread moved from a different forum section, so missing the homework template. I'm very confused about the attached questions on geometric buckling of a cylinder and a sphere. For this question I'm not given a value for the extrapolated distances (for R' and H') so I simply put the...
  18. S

    Does it irk you when journalists don't do units properly?

    I am forever reading about how this or that country had an electrical power output of so many kW in a year (just kW, not kWh). And here is an article about the volume of California sea cliffs being described in "meters"...
  19. K

    I RL circuit with polynomial forcing function solution (units)

    Hello. This is the differential equation. $$ i \cdot \dfrac{R}{L} + \dfrac{di}{dt} = t $$ My solution path: Homogenous solution: $$ r + \dfrac{R}{L} = 0 \\ \\ r = -\dfrac{R}{L} \\ \\ i_{h}(t) = C_{0} e^{ -\dfrac{R}{L} t} \\ \\ $$ Particular solution: Try $$ y_{p} = at + b \\ \\ y_{p}...
  20. R

    A Runge-Kutta: Maintaining Units in Numerical Methods

    When conducting numerical methods using 4th Order Runge-Kutta do the physical units have to be maintained? This never occurred to me until I was writing out all the steps in detail when showing someone I work with the method using a simple projectile motion with drag. It had 4th Order time...
  21. P

    I SI definition of second: what day/year is the reference year

    The SI definition of a second was originally based on 1/86 400 of a day - but the Earth's rotation is a) unsteady and b) changing so it was changed to a defined number of cycles of an atomic clock. Was there a specific day for which the atomic clock was calibrated? Put another way, why were 9...
  22. BlackJ

    When to convert units of temperature?

    Homework Statement [/B] (1)A sphere of radius 0.500 m, temperature 27.0 C, and emissivity 0.850 is located in an environment of temperature 77.0 C. At what rate does the sphere (a) emit and (b) absorb thermal radiation? (c) What is the sphere’s net rate of energy exchange? (2)A cylindrical...
  23. Arman777

    B Converting Units (Medical Application)

    I need to convert mj/mm^2 to bar is there a way to do that ? I think we cannot ,bar is N/m^2 but we have j/m^2
  24. K

    I The Relationship Between Angular and Cyclic Frequency in Fourier Transform

    Hi everybody. There has been a thread about this on physics forums, where the Fourier transform X(w) of x(t) volts (with time units in seconds) could be considered as volt second, or volt per Hz. So when we see tables of Fourier transform pairs, we might see Fourier transform plots associated...
  25. M

    B Understand Units: Physics for High School Graduating Students

    I am an student in physics department and I will graduate very soon.In my past four year I have done a good work and get a nice gpa.But as I get more and more familiar with advanced content such as quantum field theory,I become very comfusing about what I learn in my high school. Because I...
  26. P

    Natural units in the Schwarzschild Metric

    Homework Statement My Teacher says that in the Schwarzschild metric he uses natural units, where he writes ##g_{rr}=1-2M/R## He says that for one neutron star ##R=5## corresponds to approx 13 KM. Homework Equations ##1l_p=1,616 \cdot 10^{-35}m## The Attempt at a Solution Unfortunately he does...
  27. G

    Converting Electromagnetic Units: Gaussian to Superfluous Systems

    Recently, I tried to convert an energy density ##\frac{gram}{cm^3}## into ##(\frac{Volt}{cm})^2##. I faced some problems originating from the introduction of the superfluous unit ##Ampere## and its descendants in the system of units. On one hand, there are the transparent Gaussian units, in...
  28. J

    Unit conversion meters Newtons years seconds

    Hi, I need to convert a value of 12*10-16 m7 N-3 y-1 to the units of kPa-3 m2 s-1. Can anyone help me? where: m = meters, N = Newton, y = year, s = seconds. Thanks!
  29. P

    Why don't units have match for specific heat and mass

    Homework Statement A problem will ask for an amount of substance in kilograms to be raised to a certain temperature and the specific heat be given in J/g*K. The amount of substance is not required to be converted to grams to match the units in the specific heat to get the correct amount of...
  30. parazit

    I Stopping Power and Range units for charged particles

    Dear members, The unit of stopping power is given as Mev/cm in many sources. It is easy to comprehend this unit.The mass stopping power, which is the total energy lost per path length by a charged particle, is defined as the division of MeV/cm to the density of investigated material, g/cm3, and...
  31. Jezza

    I Are Planck Units Merely a Pop-Science Fad?

    As a physics undergrad, a set of natural units is nothing strange to me, we use them all the time. Having said this, I've never used Planck units. Does any area of research use them on a typical day in the office? There also seems to be this idea that I hear from time to time, perpetuated by...
  32. S

    Why does polarizability have units of volume?

    Not sure if I'm posting in the wrong place.
  33. K

    Finding the units in an algebraic equation for velocity

    Homework Statement During a short interval of time the speed v in m/s of an automobile is given by v = at^3 + bt^4 , where the time t is in seconds. The units of a and b are respectively: (a) m⋅s^2 ; m⋅s^4 (b) s^3/m; s^4/m (c) m/s^2 ; m/s^3 (d) m/s^3 ; m/s^4 (e) m/s^4 ; m/s^5 Homework...
  34. J

    Transformer cooling for Hermetically-sealed units

    Hello, I have question about transformer. How is Hermetically-sealed transformer cooled? I know that in air-breathing type we have conservator, breather, etc…for cooling. But, where the expansion oil goes in hermetically sealed? How it works?
  35. scottdave

    Insights Make Units Work for You - Comments

    Greg Bernhardt submitted a new PF Insights post Make Units Work for You Continue reading the Original PF Insights Post.
  36. D

    SI vs USC Units in Engineering

    It is well known that most of the world use the SI system of units while the USA and a couple of other countries continue to use US Customary units (ft-lb-s = FPS or in-lb-s = IPS). The question of which is better is very much a matter of personal preference, but I'd like to avoid that issue...
  37. A

    How to get the units of momentum flux?

    Good evening, Does anybody know how to get the units of momentum flux? Momentum = kg m s−1 Flux = m−2 s−1 Somehow, I should end up with kg m-1 s-1 (kg m s−1) m−2 s−1 = kg m−1 s−1 However I end up with kg m-2 s-2 Is there anybody that knows what I'm doing wrong? :)
  38. A

    What Are the Correct Units for Kepler's Third Law?

    I am confused about the units used in Kepler's 3rd law. Is T supposed to be in years or days? Is R supposed to be in kilometers or meters? Is there ever an instance where one combination of units is preferable over another (for example, if you want to use the answers from Kepler's third law to...
  39. F

    Please clear my electromagnetism doubt about units

    It is a well known fact that, in electromagnetic units, strength of a shell and strength of current flowing through its boundary are same. See here. \begin{equation} \begin{matrix} \text{i.e.}\: i \text{(biot)} = \phi \text{(biot) } \end{matrix} \tag{1} \end{equation} (a) While converting to...
  40. F

    I Why am I getting two different results in emu and SI unit?

    I am computing force between two magnetic poles each of one unit pole (in emu) and situated one centimeter apart. In electromagnetic units: ##F_{dyne}=\dfrac{p^2}{r_{cm}^2}=\dfrac{1^2}{1^2}=1 dyne## where ##p## is pole strength in emu In SI units: ##F_{N}=k_A \dfrac{P^2}{r_m^2}=10^{-7}...
  41. Q

    A How Do I Express Mass and e in Natural Units?

    Hi Everyone, I have to calculate the coefficients of the massive Higgs Lagrangian in natural units, ħ = c = 1. Do I assume firstly that, in these units the masses of the Higgs, W and Z are the usual, 125.09±0.21, 80.4, 91.2 respectively, and secondly that e has to have the value 2√(απ)...
  42. D

    Fraction within a fraction -- Units

    Homework Statement [/B] When you drink cold water, your body must expend metabolic energy in order to maintain normal body temperature ( 37.0°C ) by warming up the water in your stomach. Could drinking ice water, then, substitute for exercise as a way to “burn calories?” Suppose you expend 430...
  43. J

    Proving units for angular acceleration

    So the equation for angular acceleration on the AP physics sheet reads α = ΣT / I. I am required to prove that the units on each side are the same however I can't figure out how to get the rad/s^2 unit for angular acceleration into the same form as the right side which is N*m/ kgm^2 Any help...
  44. S

    I created a web-calculator with support for physical units

    Hi! My name is David. I'm a theoretical physicist from Stuttgart, Germany. Over the past months I have been developing an open source application called Insect, which I hope would be of interest to some of you. Insect is a high-precision scientific calculator that comes with full support for...
  45. DrClaude

    Dimensionless Units: SI Reform for Clarity & Precision

    The topic has been discussed before at PF, in particular @haruspex's Insight Can angles be assigned a dimension? Nature has now published an editorial on the subject: SI units need reform to avoid confusion
  46. L

    Problem with units for conduction rate?

    Homework Statement Consider the slab shown in Fig. 18-18. Suppose that L 25.0 cm, A 90.0 cm2, and the material is copper. If TH 125 C, TC 10.0 C, and a steady state is reached, find the conduction rate through the slab. Homework Equations Pcond = Kc *A*(TH - TC)/L K = 401 W/m*k The Attempt at...
  47. Erenjaeger

    B What is the Unit for Gas Giant Planets in Astrophysics?

    what is this unit, ⊕ ?? was reading an astrophysics book and came across it. "Gas Giant planets (>10 M⊕)" I am guessing that its mega something?
  48. Nim

    I Why Is There No SI Unit For Information?

    Why is the quantity "information" missing from the SI system? Also, if they did add it, do you think it would be added as a base unit or dimensionless derived unit?
  49. I

    Need help with gravitational acceleration SI units

    Please ignore strikeout (not sure why post is doing that) I just watched a video from Caltech (Video link at bottom of post) It says: Displacement = Distance Fallen in first second of time in [m] * Time2 so Time2 has no si unit as it is just a ratio right? Instant or Average Velocity = 2 *...
  50. 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?).
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