quantities Definition and 208 Threads

Quantity or amount is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assigning a numerical value multiple of a unit of measurement. Mass, time, distance, heat, and angle are among the familiar examples of quantitative properties.
Quantity is among the basic classes of things along with quality, substance, change, and relation. Some quantities are such by their inner nature (as number), while others function as states (properties, dimensions, attributes) of things such as heavy and light, long and short, broad and narrow, small and great, or much and little.
Under the name of multitude comes what is discontinuous and discrete and divisible ultimately into indivisibles, such as: army, fleet, flock, government, company, party, people, mess (military), chorus, crowd, and number; all which are cases of collective nouns. Under the name of magnitude comes what is continuous and unified and divisible only into smaller divisibles, such as: matter, mass, energy, liquid, material—all cases of non-collective nouns.
Along with analyzing its nature and classification, the issues of quantity involve such closely related topics as dimensionality, equality, proportion, the measurements of quantities, the units of measurements, number and numbering systems, the types of numbers and their relations to each other as numerical ratios.

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  1. pellman

    How do we associate real measurements with theoretical quantities?

    Let us take for granted for this discussion that we are clear by what we mean by macroscopic measurements: reading a number from a ruler, a scale, a gauge of any sort. Now suppose we perform a (macro) measurement of some aspect of a real laboratory system whose result, we presume, depends on...
  2. N

    Which one of the quantities below has dimensions equal to ML/T^2?

    Homework Statement Which one of the quantities below has dimensions equal to [ML/T2]? Homework Equations a. mv b. mv2 c. mv2/r d. mvr e. mv2/r2 The Attempt at a Solution I know that ML/T2 is for calculating force for circular motion (I believe) Therefore after breaking it...
  3. Z

    Why are no DIVERGENT quantities (infinities) in String Theory ?

    Why are no DIVERGENT quantities (infinities) in String Theory ?? why String theory is FREE of infinities ?? ... why there are no divergent integrals in string theory whereas in normal Quantum Field theory there are infinities ??
  4. S

    Radiometric Quantities: Physics of EM Wave Explained

    Hello everyone, I'm hoping someone can help me understand (in a most general fashion possible) a relations between radiometric quantities and physics of EM wave. With EM wave quantities that are usually mentioned in books (at least the ones I've found) are: - energy density of EM wave...
  5. S

    Confusion over real and complex versions of the same quantities

    Some authors speak of the ``index of refraction'' and the ``relative permittivity'' (or ``dielectric constant'') as real numbers, as if they do not warrant any discussion of complex numbers. Other authors speak of the ``complex index of refraction'' and the ``complex permittivity.'' But they all...
  6. B

    Mixing three water quantities at different temperatures

    I am trying to figure out the following in my beer brewing. I have been able to find equations for mixing two quantities of water, but not three. Can anyone help me out here? So, I have 5 liters at 100 C and I want to add 18 liters (x at 20 C and y at 8 C) to arrive at 23 liters at 24 C. This...
  7. fluidistic

    Lagrangian of a particle + conserved quantities

    Homework Statement Consider the spherical pendulum. In other words a particle with mass m constrained to move over the surface of a sphere of radius R, under the gravitational acceleration \vec g. 1)Write the Lagrangian in spherical coordinates (r, \phi, \theta) and write the cyclical...
  8. fluidistic

    Equation of trajetory+conserved quantities of a motion over a sphere

    Homework Statement Determine the equation of the trajectory and the conserved quantities in the motion of a particle constrained to move freely over the surface of a sphere.Homework Equations Not sure. The Attempt at a Solution I think it is convenient to use spherical coordinates (r, \phi ...
  9. A

    Solving Quantities and Units Homework as an Access Student

    Homework Statement I'm stuck on 3 questions from my assignment as an access student (I never studied science before) First thing is: Explain the term " centre of gravity" and where it is in relation to a metre rule. Second: A metre rule is pivoted at its 10cm mark. A 1N force is...
  10. Q

    Lagrangians and conserved quantities

    Hi, I have a relatively straight forward question. If we have a Lagrangian that only depends on time and the position coordinate (and its derivative), how can I decide whether angular momentum is conserved? That is, if the Lagrangian specifically does not have theta or phi dependence, does...
  11. S

    Formulating Physical Quantities, Energy & Conservation of Energy

    1. Homework Statement Hi, I've been thinking about a formulation regarding "physical quantities" (that is, the quantities that specifically constitute the object of measurement for Physics), energy, and the conservation of energy. It would be very helpful for me that you could confirm me...
  12. Char. Limit

    Vector Quantities: Can Unit of Measurement Reveal Vector?

    Can someone tell, using the unit of a physical measurement, if the measurement is a vector? For example, without knowing about force, can one tell by the unit kg-m/s^2 that force is a vector? I'm trying to say, for example, thay since the m in kg-m/s^2 is a vector (for example), the whole...
  13. M

    Galilean invariance and conserved quantities

    Hi I have a simple question what is the conserved quantity corresponding to the symmetry of galilean invariance? and Lorentz invariance? cheers M
  14. M

    How to Create Vector Notations in Microsoft Word 2007?

    Hi, Do anyone know how I could make vector quantities in Microsoft Word 07, for example something like F = ma, I want a vector notation on F and a. Please be as specific as you can. Thanks
  15. S

    Sites where I can purchase small quantities of components?

    Does anyone know of any sites where I can buy components like ICs or off-the-shelf stuff like resistors and capacitors in small amounts (<10, for example?). The only one I know of is jameco.com, and they don't have one of the ICs I'm looking for (LM2678T-12). Any others?
  16. E

    Physical Meaning of Mathematical Quantities

    Hello, What is the physical meanining of rational and irrational numbers? In the same sense, what is the physical meanining of complex quantities? Thanks in advance
  17. B

    Quantities describing time-dependent phenomena measurable initially?

    I've been thinking about a physics problem where one can determine information about a time-dependent phenomena from looking at some quantity at one instance in time. (I'm not talking about a conserved quantity such as energy.) In my case, we are considering a wave problem and the quantity is an...
  18. R

    Are Current, Potential, and Potential Difference Scalar or Vector Quantities?

    Hi Just wondering if someone can tell me if the following are scalar or vector quantities and why Current Potential Potential Difference Also, I'm wondering if we include plus/minus signs in calculations depending on the charge. Ex. would current be negative if it was a negative...
  19. O

    Humans emit very small quantities of light

    http://news.yahoo.com/s/livescience/20090722/sc_livescience/strangehumansglowinvisiblelight Weeird! But awesome.
  20. M

    Feel of physical quantities - help

    Homework Statement how can i have a feel of pressure ... i mean how much is 1 psi and how much is 10 psi pressure ... can you please give an example ! Homework Equations i think pressure = force / area but still i don't undersatnd how much is 1 Newton ... i mean i don't get a feel of...
  21. D

    How Far Does the Student Swim Across the River?

    1. In still water, a student can swim at 1.2 m/s. She swims perpendicularly across a 40 m wide river, landing 30 m downstream. In crossing the river, what distance does the student move? 2. d=df-di, cosine, sine, tangent 3. Again, i tried drawing out a picture. I made 40m the x...
  22. S

    Having Trouble Converting Units?

    i have problems converting quantities, like for example Km/h to metres per second, or Days to seconds. I realize it involves multiple multiplications or division but for some reason i still have trouble with this relatively simple concept. In some cases, i even get the final answer wrong because...
  23. Goddar

    Determine thermodynamics quantities with 1 data

    Homework Statement Each molecule of a certain substance can exist in either of two states; these states differ in energy by 25 eV. a. If one mole is in equilibrium at room temperature, what is the fraction of atoms in the excited state? b. What is the entropy of this sample at room...
  24. T

    Partition Theory of Nitrigen to determine ther quantities (eg U, H, F)

    Homework Statement For a mole of nitrogen (N2) gas at room temperature and atmospheric pressure, compute the following: U, H, F, G, S and μ. The internal partition function is purely rotational, and the rotational constant ε for N2 is 0.00025 eV. The electronic ground state is not...
  25. M

    So, what is the deal with differentials and infinitesimals in physics?

    I'm currently taking several physics courses (mechanics, thermodynamics etc) and common to them all is their frequent use of infinitesimals. I'll just give a short recap of how I was taught calculus, and this is how my math teacher would word it: [calculus training] \frac{dy}{dx} is not a...
  26. M

    Why would large quantities of dark matter not stick together ?

    Does dark matter form orbits around stars ? Why would dark matter and "regular" matter, say, a dust belt not mingle and stick together? Just with black holes, with d.matter we are positing new objects with complex properties instead of simply admitting imperfection in gravity. Since it is...
  27. Peeter

    Conserved Quantities from Boost/Rotation of Maxwell Lagrangian

    I've calculated the conserved quantity for a boost or rotation of the Maxwell Lagrangian using the field form of Noether's theorem. If I calculated right, the components of a conserved four vector "current" considering boosts along in the x-axis appear to be: C^\mu = \eta^{\mu\nu} (F_{\nu 0}...
  28. Q

    Differential geometry in quantum mechanics - conserved quantities

    Hi everyone. This is kind of a geometry/quantum mechanics question (hope this is the right place to post this). So, in quantum mechanics we consider operators that reside in an infinite dimensional Hilbert space (to speak rather informally). We even have the cool commutator relation, which is...
  29. B

    Conserved quantities for geodesics

    Homework Statement In comoving coordinates, a one dimensional expanding flat universe has a metric ds^2 = -c^2dt^2 + at(t)^2dr^2. Derive an expression for a conserved quantity for geodesics in terms of a, \tau and r, where \tau is the time measured in the rest frame of the freely falling...
  30. D

    Comparison between 2 or more quantities

    Hi everyone, I need your help badly. This may sound simple to everyone but I need to get the concept sorted out. For ratios, we know that it is a comparison between 2 or more quantities with the same units. My question is, can ratio be used to compare between say ingredients in a...
  31. M

    Exploring the Discontinuity of Fundamental Quantities and Calculus

    i wondered at the idea that calculus works for continuous functions and in reality fundamental quantities are discontinuous. For example energy or an electron can't asume all values. Therefore isn't there a conflict when we work on a equation like dE/dt or something similar which involve...
  32. L

    How do i find quantities in fusion formulae

    in the equation *C^12+C^12-->Mg^24+y(+13.93 MeV)* for what quantity is the energy assigned? and how would i plug in a certain amount of carbon?
  33. M

    Fourier series technique to show that the following series sum to the quantities

    Use the Fourier series technique to show that the following series sum to the quantities shown: 1+1/3^2+1/5^2+...+1/n^2=pi^2/8 for n going to infinity I foudn the series to be: sum(1/(2n-1)^2,n,1,infinity) but I don't know how to prove the idenity. I don't know how to go about...
  34. A

    Conserved Quantities in de Sitter ST

    [SOLVED] Conserved Quantities Question answered!
  35. H

    Infinitely many integrable/conserved quantities? Soliton?

    Hi all. I would like to know what's so special about those "integratable systems"? I heard that KdV and NLS models belong to these systems and so they have soliton solution? But why? What's the importance of this? And what's the significance of many conserved quantities? I know, say, KdV has...
  36. P

    Symmetries and conserved quantities

    I know that if a particle is in a spherically symetric potential its angular momentum will be conserved, but what about if somehow we manage to produce say an elliptically symmetric potential? Will the particle then have a momentum along the curve of the ellipse conserved? Thanks
  37. B

    Invariance of combinations of physical quantities

    Please tell me if there are motivated physical reasons to consider that combinations of dimensionless physical quantities that appear at the exponent of e in distribution functions have the same magnitude in all inertial reference frames in relative motion, Thanks in advance
  38. L

    What are the differences between scalar and vector quantities?

    Hmm... I don't know the differences between the scalar and vector quantities? Help, please? I don't want to fail physics!
  39. 0

    Why dimensions can be treated as algebraic quantities?

    Hi, in my physics book (serway) they say "dimensions can be treated as algebraic quantities" but I don't understand this very well. If I sum meters I get meters, if I multiply meters I think I get meters^2 because the area of a rectangle is b.h. But if, for instance, I multiply seconds.seconds...
  40. V

    Why are Planck quantities so extreme?

    Why are Planck quantities considered to be maximum and minimum quantities - Planck distance etc ? If they are,then,since in calculus a maximim/minimum is given by,for example,dy/dx = 0,then,for example,y = Planck quantity when x = some other quantity.But what is x?
  41. R

    Understanding Vector and Scalar Quantities in Physics

    No, I am not going to ask you what the difference between those two are. =P I know the differences, but at the beginning of this term, my class started to learn about electricity and magnets, and that stuff. Now, vector quantities are those that have direction and scalars are those without...
  42. E

    What does quantities and dimensions mean?

    i would like to ask a question about what does quantities and dimension mean in this sentence is it possible for two quantities to have the same dimensions but different units? thanks a lot in advance
  43. Mentz114

    Invariant quantities in the EM field

    I understand that the quantities E^2 - B^2 \vec{E} \cdot \vec{B} (the dot is vector inner product). where E and B are the electric and magnetic components of an EM wave, are invariant under Lorentz/Poincare transformations. Can someone explain the physical significance of this ? Is...
  44. M

    How Fast Do Bristles on an Electric Toothbrush Move?

    Electric toothbrushes can be effective in removing dental plaque. One model consists of a head 1.10 cm in diameter that rotates back and forth through a 70.0 degree angle 7600 times/min. The rim of the head contains a thin row of bristles. Part A: What is the average angular speed in...
  45. A

    Invariant quantities for antimatter

    Since antiparticles have reversed proper time, can I conclude that all invariants are reversed for antiparticles?
  46. P

    Quantities as an ordinary decimal number

    Express the following quantities as an ordinary decimal number: a) The sun has a diameter of 1.392 * 10^6 I get 1392000. b) 8.4*10^-6 I get 0.000084 Is this right
  47. M

    Is Angular Momentum of z and Energy Conserved?

    hi, if i have mass possesses potential U(x)=-Gm1m2/(x^2+y^2+(kz)^2 )^1/2 , i said angular momentum of z is conserved but not angular momentum of x , y .. is it correct ? what else is conserved ? energy ?
  48. I

    Vector Addition of differing quantities

    My girlfriend had this problem on her first tutorial sheet at Univeristy. She is doing maths. I am doing physics and was interested in the answer. It asked what the result was when a displacement vector was added to a velocity vector. The vector addition can obviously be done on these two...
  49. A

    How Do You Calculate the Mass of Water Produced in a Chemical Reaction?

    i have no idea how to do excess and limiting (mole conversions) does this concept even apply to this Question and how to figure out this out? if 10 g of ammonia gas reacted with 5 g of Oxygen gas, what mass of water is produced? using this eqn: NH3 + O2 --> NO2 + H2O
  50. F

    Number of basic physical quantities

    Recently, I was thinking about this: Am I right if I say that there are only 4 (and exactly 4) basic physical quantities which are enough to explain all observed phenomena in nature? (of course I mean HOW, not why) (for example length, time, mass and electric charge or current)...
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