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. L

    What are the standard units for inertial mass and gravitational mass?

    [SOLVED] What are the standard units for inertial mass and gravitational mass? 1. What are the standard units for inertial mass and gravitational mass? And also apparently gravitational mass can be measured without gravity how can it be done? Thank you very much. My teacher said a hint is in...
  2. A

    Struggling With Physics: Units of Periods Needed

    I've just been introduced to wavelengths and so forth in my Physics class but i was out for 3 weeks and I'm basically expected to do all these equations and homework with no help or anything. Can't contract my professor, it's winter break and I've tried researching but i can't find what the...
  3. F

    Why do we still use seconds and meters as SI base units?

    If The second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. And The meter is defined as 1⁄299 792 458 of a light-second. Then Why can't we...
  4. stevebd1

    Lambda-CDM model and geometric units

    I'm currently putting together a basic summary of the Lambda-CDM model and I have a slight issue with the fact that the equation to calculate lambda (which includes factors to convert physical units into geometric units) is incorporated into the omega_lambda calculation (which incorporates the...
  5. K

    Wat are the units of angular velocity of precession?

    Homework Statement What are the units of angular velocity of precession? I've looked evrywhere and can't find out. Homework Equations The Attempt at a Solution In my answer to a question, by putting units into the equation i think I am getting units as rad^-1 s^-1 but not sure...
  6. P

    What Are the Correct Units for Weight?

    Homework Statement The units for weight are A)kg B) Newtons c) kg(m/s^2), the 2 means squared d) both b and c Homework Equations The Attempt at a Solution i believe the the answer is d am i right?
  7. L

    Modern Definition of Time & Length Units

    a) What is the modern definition of the time unit and the length unit? b) How people actually Materially realize these units ? (a) in the wiki, it reads: Second: Under the International System of Units, the second is currently defined as the duration of 9,192,631,770 periods of the...
  8. P

    Solving the Question of Units for Dropped Mass on Surface

    I *think* this is right, but if there is something obviously wrong please tell me where Ive got a mass of weight 'y' dropped onto a surface that can support 10y there is no wind resistance the mass starts from stationary and accelerates under gravity (assumed to be 9.8 m/s/s) the...
  9. R

    Synchrotron Radiation Units: Photons/s/mrad^2/1%BW

    Hi I have a question about the common unit for the intensity of a synchrotron X-Ray spectrum: \frac{Photons}{sec*mrad^{2}*0.1\%BW} I am not sure how to interpretate the 0.1%BW. How do I get the numbers of Photons/sec/mrad2 in an Energy range lets say from energy E_1 to energy E_2...
  10. S

    What Does 'Per MeV' Mean in Muon Energy Loss Calculations?

    I have a problem with units... I have been looking at energy loss of muons in matter (from both ionizations and radition processes like bremsstrahlung). I have used an equation for the mean energy loss (for a muon of specified energy in a specified material) which gives an answer in units of...
  11. X

    Can Work Be Expressed In lb x lbf Units?

    Can work be expressed in the units lb times lbf?
  12. P

    Surely k-calculus kT is 'mixing units'

    Hi, This is my first post, so hello everyone! I just have a quick question about the k-calculus, and am using the 2nd diagram on http://www.geocities.com/ResearchTriangle/System/8956/Bondi/intro.htm as a reference since it is the same one as in the book i am reading from. In the...
  13. M

    Finally a replacement for SI units

    Finally after man(and woman)fully resisting the urge to go fully metric for 30years the UK's boffins have produced an alternative system of units, even more brilliant then the venerable Firkin/Fortnight/Furlong system. The velocity of a sheep in a vacuum is 26.22 kilobrontosauruses per...
  14. E

    What are the units of the probability flux j?

    Homework Statement What are the units of the probability flux j? \vec j = \frac{\hbar}{2mi}\left(\Psi^* \vec \nabla \Psi - \Psi \vec \nabla \Psi^*\right) Homework Equations The Attempt at a Solution The units of psi are probability amplitude and the units of del(psi) are...
  15. G

    Frequency in units of inverse length?

    Hi, when someone gives me an angular frequency in units of inverse length (i.e., 520.5 cm^-1) how do I convert that to a frequency and and energy (say, in eV?). Thanks for the help!
  16. A

    Convert British and SI Units Easily

    hey can anyone give a calculator(like any html link) or something of that sort which can convert units, like from british system to SI units and vice versa. looking at the tables everytime is sooooo boring and i am fed up of it.for eg. changing lengths, pressure, weight etc. etc.:-p:-p
  17. B

    Understanding Pressure: Definitions and Units

    Homework Statement Which of the following definitions or units apply to pressure? True False Newtons per square meter True False kg per cubic meter True False pascals True False force per unit area True False mass per unit volume The Attempt at a Solution My answers are in...
  18. S

    FAQ:What's the differences between Radiometric Units and Photometric Units?

    What's the differences between Radiometric Units and Photometric Units?
  19. F

    How Do You Convert Micrometers to Meters?

    This isn't an actual problem in my text so I won't be using the usual template to ask it, just a quick clarification question: According to a chart in my text, a micro is 10^-6. So if I had, say... 20 micrometers of something and wanted to convert to meters... wouldn't that just be 20E-6 meters?
  20. G

    Bernoullis equation and appropriate units

    I've just completed a question using Bernoullis equation but I am unsure of what units I should give the answer in. By taking the units of the terms in the equation to be Pressure density velocity density acceleration height Nm^2 Kg m^-3 m s^-1 Kg...
  21. A

    Questions about units and conversion

    When you solve a problem and it wants the answer in non-SI units and they given you non-SI units, do you need to convert the non-SI units to SI units before you plug them into equations such as x=1/2gt^2. If you don't convert them into SI units, you'll get the answer wrong right? Basically...
  22. F

    Derivations of SI Units in my High-School Physics formulas.

    I was bored so I make fun with derivations of SI units of many Physics formulas. Note, this should just be called "introductory physics", that means NO calculus (but rate of change designated by the delta symbol) and motion is in one or two directions only. This is high school physics level in...
  23. K

    Can you give a more specific question?

    Homework Statement Find 2 unit vectors u1, u2, lying in the plane, x-y+z=0, which are not parallel to each other. The Attempt at a Solution I've tried taking the unit vector of the normal vector <1,-1,1> which is <1/rad(3),-1/rad(3),1/rad(3)>, but my teacher has told me it is not in...
  24. R

    Abstract Algebra: M(R) 2x2, units, where does the determinant come from?

    Homework Statement Prove that (a b c d) is a unit in the ring M(R) if and only if ad-bc !=0. In this case, verify that its inverse is (d/t -b/t -c/t a/t) where t= ad-bc. Homework Equations An element a in a ring R with identity is called...
  25. P

    Waves: String Physics? Correct my units

    Waves: String Physics?? Correct my units.. Homework Statement The velocity of a wave on a string depends on how hard the string is stretched and on the mass per unit length of the string. If T is the force exerted on the string and Mu is the mass/unit length, then velocity v is...
  26. C

    Radiometric and Photometric units

    There seem to plenty of threads dealing with questions on topics such as "brightness" and how the human eye perceives objects under certain circumstances, so I've written up a mini-tutorial on how physicists quantify these concepts. 1. Radiometry and Photometry Radiometry is the measurement of...
  27. M

    Problem with natural units in Cosmology

    Homework Statement Reading about the raditation dominated era I saw that the radiation energy density today was given by: \rho_r = \frac{\pi^2}{30} g_* T^4 = 8.09 * 10^{-34} g/cm^3 where g_*=3.36 is the degree of freedom of the radiation (equivalent) and T=2.75 K is the CBR...
  28. tony873004

    Work problem. Right answer, wrong units

    My answer should obviously be in Newtons, but I'm getting Netwon meters. An aquarium, 2 m long, 1 m wide, and 1 m deep is full of water. Find the work needed to pump half the water out of the aquarium. (The density of water is 1000 kg/m3.) In a similar example in the book, they do the...
  29. S

    Are Tensions Represented as Unit Vectors in Physics Problems?

    Homework Statement See Attachment Homework Equations The Attempt at a Solution Im just trying to figure out all of the forces, I am kinda confused about the whole T_{BDC} Do i just make these two separate tensions...and then add them together or something? Can someone explain...
  30. P

    Ozone Concentration: 25 Dobson Units

    Homework Statement If the ozone concentration in a particular sample of air were 25 dobson units, what sould this concentration be in: a)ppm b) %(v/v)Homework Equations 1 dob = 2.69*10^20 ozone molecules / m^2 http://en.wikipedia.org/wiki/OzoneThe Attempt at a Solution The question is asking...
  31. DaveC426913

    Unlocking Blood Test Volume Units: E9, E12 & More

    I just got my blood test back and the numbers have some units I don't recognize, such as E9 and E12. The printer seems to not be able to handle very sophisticated formatting, for example: - one unit is listed as "UMOL/L" for Creatinine. I suspect that this is meant to be \mumols. -...
  32. S

    CGS Units in Physics: Use & Benefits

    Up until my third year EM course we have used SI and MKS units in EM. In fact every textbook i have used for EM (griffiths,wangsness) also use those units. My current prof wants up to learn CGS units. While they do appear much 'cleaner' (no epsilon0, mu0 for certain equations) what is their...
  33. Repetit

    Logarithm of numbers with units

    Hey! I have always learned that functions like logarithms, exponentials, trigonometrics etc. have to operatore on pure numbers and not numbers with units. For instance, you cannot write: Sin ( 5 kg*m/s^2 ) But in chemistry I often find formulas where logarithmes of numbers with units...
  34. G

    Inverses of Units: Are All Conjugates Always in the Field?

    Okay, if we are looking at a typical extended number field Q(w), and it's corresponding ring of integers, we know that for any given element in this field, it is not necessary that all of it's conjugates are in the same field. A typical example being: Q(\theta), \theta=\root 3\of{3}, \theta...
  35. S

    Using CGS or SI Units: When to Choose?

    I have a simple question. I understand the quantitative differences between cgs and SI units, but when will I be expected to use one over the other? For example, do physicists prefer one set of units? Thanks for the help.
  36. T

    Expressing second and its derivatives in terms of seven SI base units

    Time-oriented geometrized units→Second and its derivates in terms of 7 SI base units I expressed second in terms of meter and kilogram. For doing this I used: For expressing second in meters: 1s¹ = c = 299792458 m For expressing second in kilograms: 1s¹ = c³/G =...
  37. DaveC426913

    Where Can I Find Authoritative Sources for International Volume Units?

    I'm editing a school textbook and have suddenly discovered at the 11th hour that there is a difference between the U.S. cup (236ml), the Canadian cup (227ml) and the British cup (284ml) as well as conflicting results (such as Wiki) that define them differently again - U.S.=250ml, Canadian=240ml...
  38. S

    Different units in Bernoulli's equation's terms?

    When I check units in the terms in Bernoulli's equation, they do not match: Given: p1 + 1/2 (row) v1^2 = p2 + 1/2 (row) v2^2 On the left hand side of the equation, the first term, pressure must have units of force/unit area; say lb/ft^2. The units in the second term are the product...
  39. U

    Electric Field Strength H Units - Ampere Turns/Meter?

    What are the units of the electric field strength H? I know that H = NI/L for a solenoid and I'm wondering if there is any condensed unit or if it is just ampere turns per meter.
  40. tony873004

    What is 2D Density? Understanding Mass, Volume, and Area in Relation to Density

    density is (mass / volume). But what is (mass / area)? For example, if I wanted to know the mass of how much water would fill a jar, it would be mass = (volume of jar * density of water) = cubic length * (mass / cubic length.) But imagine I knew how much a square meter of paint weighed...
  41. DaveC426913

    E=mc^2 in Natural Units: Understanding the Meaning of c^2

    Somewhere a month or two ago, there was a discussion about E=mc^2 and the question of what the c^2 represents. The answer was that c^2 was simply a conversion unit, to put it in more common units of kg, m and s. That, if the formula were considered in more natural distance units of light...
  42. C

    How to Use SI Units in Equations for Scientists

    Hi Everyone, I think I posted this message to the wrong forum, so second try... I hope this is the right one? Could someone please explain to me how I know when to use SI units to solve a problem and how to enter these units into an equation - are there any rules of thumb? If I could get a...
  43. M

    Figuring out the units for the cosmological constant

    How does one figure out the units of measure for the cosmological constant? In the Einstein Field Equation: \[Rab - \frac{1}{2}Rgab + \Lambda gab = 8\pi Tab\] Lambda is a constant but the units of measure for gab and Tab differ for each combination of indices. For example T00 is an...
  44. J

    Question regarding System of Units

    Im following a British curriculum for high schools ( known as A levels ) . I am reading stuff from this forum and i come across differences in notation used by the British and the Americans ... plus differences in units ... why is this so ? why couldn't u guys settle on one universal system of...
  45. G

    Finding units in polynomial quotient rings

    Is there a simple method for finding all the units in a polynomial quotient ring over a finite field? For example: {F_2[x] \over x^7-1} I can see the easy ones like 1, and all power of x, but I wanted a general rule or method for finding all of them if it exists (besides testing each...
  46. R

    Valid Units of Measure for Trig Argument

    Quick question. If i pass into a trig function something like cos(3pi*15 seconds), do I drop the seconds from the resultant answer since it's not a valid unit of measure for theta?
  47. M

    Probability Units: Mean, Mode, Median, Variance, SD?

    hihi for example, I am doing a question involving the probability of the number of apples i eat in a day. i need to find the mean, mode, median, variance and standard deviation. do these values need to be in units of apples? or just like a numerical value such as 2.3 ? thanks
  48. E

    Convert Units: Help Appreciated!

    Can anyone help? I don't understand how to do this for example: how many cm cubed are in 1 metre cubed? I am really stuck, your help would be appreicated. Thanks in advance.
  49. P

    Acceleration of an Object in g Units

    Question: An object is moving on land at a speed of 1020 km/h. This object goes from full speed to a complete stop in 1.4 seconds. In g units, what acceleration did the object 'experience' while stopping? My guess is I have to plug in -9.8 m/s into this equation, but I'm not sure how. Any...
  50. B

    AS Physics course on units help

    I have just started the AS Physics course and we have been doing base units, base quanntities, derived units and drived quantities. This stuff completely baffles me, and cannot find a site which explains this stuff in bog standard english. Please could someone help me. Thanks, Ben
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