What is quantities: Definition and 207 Discussions

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. P

    Finding Conserved Quantities of a Given Lagrangian

    Homework Statement Find two independent conserved quantities for a system with Lagrangian L = A\dot{q}^{2}_{1} + B\dot{q_{1}}\dot{q_{2}} + C\dot{q}^{2}_{2} - D(2q_{1}-q_{2})^{4}\dot{q_{2}} where A, B, C, and D are constants. Homework Equations None.The Attempt at a Solution I've only found...
  2. A

    Confused about thermodynamic quantities and their minimums.

    http://img842.imageshack.us/img842/7200/img0103iu.jpg Mainly concerned with the first half of the page. You'll see that it derives for a system in contact with a constant-temperature, constant-pressure heat bath that the change in Gibbs entropy is always less than or equal to zero. Equality...
  3. S

    Extensive and intensive quantities

    What are the difference between extensive and intensive quantities?
  4. R

    Hydrogen Fluoride gas mixture quantities

    Hi, I am not a chemist but maybe there is somebody who can help me. I need a put together an emergency plan as part of a college law assignment on European Seveso directives. My case study has 17t of Hydrogen and 8t of Fluorine. Both of which combine satisfy the requirement for a lower...
  5. B

    Why is torque perpendicular to the plane of rotation in rotational motion?

    Hello, Of the different rotational quantities of motion--angular velocity, angular acceleration, torque, angular momentum, etc.--, which of them has their direction perpendicular to the plane of rotation (not sure if I worded that correctly)? I am pretty certain that torque has its...
  6. D

    Need help deriving multiple quantities

    Need help differentiating multiple quantities Homework Statement f′(x) = (x − 1)(x − 2)^2(x − 3)^3(x − 4)^4(x − 5)^5 I need help in trying to differentiate this equation. I know could use a combination of the chain and product rule to figure it out, but my teacher said that doing so would...
  7. B

    Help with finding missing quantities on Free-Body Diagrams

    Homework Statement Fill in the missing quantity for the following: V = constant FNet = ? a = ? F1 = ?Homework Equations FNet = Fn - Fg + Fa - FF Fg = mg FNet = maThe Attempt at a Solution Because I honestly do not know how to go about solving this, the only things I've done are review class...
  8. A

    Conserved quantities in mechanics

    So having been through translation and rotation I can conclude that my book has found 3 conserved quantities in classical dynamics: Energy Angular momentum Momentum That is 7 separate quantities which are conserved E,Lx,Ly,Lz,px,py,pz But this question is bothering me: How do we know that...
  9. X

    Dimension Of Physical Quantities

    Hi All PF Members... I'm New to this website.. Also new to physics... nd I'm very exited about this aweSome website...where I can post my problems... Experts I want list of All physical quantities and their Dimension... I've been searching and cannot find any thing good enough... Sorry for my...
  10. A

    Thermodynamic Processes: Adiabatic/Isochoric/Isobaric/Isothermal

    Adiabatic process: a process where no heat is gained or lost. it is my understanding, however, that this is a hypothetical system. There is no insulator on Earth good enough to allow this system to exist, except to approximations. So, what happens is you have a system where whatever is...
  11. Y

    Relationship of Physical Quantities in Functions

    Homework Statement This is actually a part of my physics lab assignment, but there isn't any physics involved here, so I chose to post this here. I hope that isn't a problem. Anyway, I've been given three data tables, and have been asked to make graphs for each of the data tables by hand...
  12. O

    Help calculating energy quantities using spectroscopic constants?

    Hi, I'm a new AE Ph.D. student in the field of supersonic mixing and combustion, currently making preparations for ordering equipment necessary to perform Filtered Rayleigh Scattering measurements in our tunnel. At this point, I am implementing a model for predicting the shape of the...
  13. O

    Can someone explain conserved quantities in this activity

    Hello, Can Someone help me with this activity - http://www.particleadventure.org/other/education/five_s.html - its activity 5 The rules of the Game The answer to the activity is - http://www.particleadventure.org/other/education/five_s.html I don't understand how they got the answer for...
  14. M

    Physical Quantities: Distinguishing Scalars & Vectors

    How can we distinguish scalars from vectors?If we are given a certain physical quantity how can we justify whether it is scalar or vector?
  15. K

    Dimensionless Numbers in Heat Transfer

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  16. A

    Unit vectors and vector quantities (notation)

    When you write vector quantities with unit vectors, do you still have to draw an arrow on top to indicate that it's a vector? e.g. velocity and acceleration. My textbook doesn't have it bolded so does that mean they're just taking the magnitude and then multiplying by the unit vector to make it...
  17. ShayanJ

    How Do Velocity and Displacement Vectors Transform in Plane Polar Coordinates?

    Consider the velocity vector v^i=\dot{x}^i \hat{e}_i . We know that in the plane polar coordinates,it becomes \vec{v}=\dot{r}\hat{r}+r\dot{\theta}\hat{\theta} We also know that it is a contravariant vector so if we transform it covariantly from cartesian coordinates to plane polar...
  18. R

    Are Scalar Quantities in Physics really 1-D Affine Spaces in disguise?

    In Physics it seems quantities are either Scalars or Vectors (let's not get into tensors, but if there are other types, please tell me). Vectors I understand reasonably well. Scalars, however, I'm not so sure about: Consider the Scalar quantity of Temperature. There is absolute zero, but...
  19. P

    Why are Some Constants Dimensionless?

    Why are pure numbers like 1 , 2 , 3 ... dimensionless and Avogadro's Number, Plank's Constant, Gravitational Constant dimensional ?
  20. J

    Translating scalar torque quantities to their vector analogues (RE: Dipoles)

    My question is at the bottom of this post PREAMBLE: If a dipole is turned by an angle θ (in a uniform electric field) then the torque applied on the dipole by the electric field will be: τ = 2.q.a.E.sin(-θ) = -2.q.a.E.sin(θ) with the negative sign referring to it being a "restoring" torque...
  21. m4r35n357

    Conserved quantities in the Doran Metric?

    I've been doing some amateur simulations of particle trajectories in a few well-known metrics (using GNU Octave and Maxima), and in the case of the Schwarzschild and Gullstrand-Painleve metrics I have the ability to check my results using freely available equations for conservation of energy and...
  22. F

    Symmetry Groups Algebras Commutators Conserved Quantities

    Symmetry, Groups, Algebras, Commutators, Conserved Quantities OK, maybe this is asking too much, hopefully not. I'm trying to understand the connection between all of these constructions. I wonder if a summary about these interrelationship can be given. If I understand what I'm reading, there...
  23. K

    Showing different physics quantities of a drum pad

    Hey, atm I'm working on a physics project for school where we pick an instrument and answer questions about it that we'll have to present in class. I'm going to use a drum pad. The one question I'm stuck on is: I'm not sure if this would be right but please correct me if I'm wrong: For...
  24. D

    Why are quantities called operators

    Is it because measurement of those quantities involves action on the system. And is the idea that as light is to be used to measure momentum which effects its position fundamental of QM or is it merely like an analog to understand.
  25. D

    Nondimensional substitutions for Insect Outbreak Model

    The DE is Insect Outbreak Model: Spruce Budworn with Ludwig's predation model \frac{dN}{dt}=r_BN\left(1-\frac{N}{K_B}\right)-\frac{BN^2}{A^2+N^2} r_B is the linear birth rate K_B is the carrying capacity The last term is predation A is the threshold where predation is switched on...
  26. K

    Connection between the generators of the Galilean group and physical quantities

    How can I see that the generators of the Galilean group correspond to energy, momentum, etc.? References which cover the Galilean group and algebra as well as their realization in phase space are appreciated, especially if they are not too sophisticated. Thanks kith
  27. B

    Describing quantities independently from frames in Newtonian mechanics

    Hello I know that it's possible to reformulate Newtonian mechanics in such a manner that absolute velocities of objects can be defined. By absolute I mean defined without any reference to a specific frame of reference (just as in the article Notes on Mathematical Physics for Mathematicians)...
  28. D

    What makes 37 a unique and special number?

    what is the most important fundamental quantity
  29. J

    Dimensionless physical quantities

    Hi:) A question that I don't understand, and my feeble attempt to answer it. Can anybody give any heads up on this one? If a physical quantity is dimensionless, it has no units attatched to it. Determine if the following constant is dimensionless and show your reasoning" \alpha=...
  30. X

    Find Kmax with given numerical quantities

    Homework Statement K(max) = (6.63x10^-34 J s)(7.09x10^14s) - 2.17x10^-19J solve for kmax Homework Equations none? The Attempt at a Solution K = (6.63x10^-34 J s)(7.09x10^14 s) - (2.17x10^-19 J) K = (6.63)(7.09)(10^-34)(10^14) J s^2 - (2.17x10^-19 J) K = (47.0067)(10^-24) J s^2...
  31. G

    Physical quantities/ magnitudes

    I've seen that in English you refer to the measurable physical properties as http://en.wikipedia.org/wiki/Physical_quantity" , but some sites call them "physical magnitudes". Are both of them correct?. Do you consider them as synonyms? In Spanish we say "magnitudes físicas", and I wonder if...
  32. K

    Measured vs calculated quantities

    Hello everyone, My general goal is to understand why and how certain physical formulas came to be written, a specific way and not another - so as to judge their correspondence with reality. My specific interest in this thread is to understand the link between a formula(calculated or complex...
  33. J

    Mathematica Small quantities in mathematica

    "Small" quantities in mathematica Hi, I'm doing a calculation in which I have a small parameter \epsilon floating around, and I want to automatically remove terms of order \epsilon^2 and higher. Is this possible to do?
  34. M

    How to recover comoving quantities

    Hi, I have a little problem, I'm using a code to run cosmological simulation and I have to recover the physical unities of every quantities. The problem is that there isn't a proper guide for this program. I try to explain. All I have for every output/redshift is: aexp unit_l unit_t The...
  35. fluidistic

    Equations of motion of a particle over a cone+conserved quantities

    Homework Statement Exactly the same problem as https://www.physicsforums.com/showthread.php?p=3335113#post3335113 but instead of a cylinder, the surface is a cone.Homework Equations Same as previous thread. The Attempt at a Solution I used cylindrical coordinates (r, \phi , z). By intuition I...
  36. fluidistic

    Equations of motion of a particle over a cylinder+conserved quantities

    Homework Statement I must determine the conserved quantities+the equations of motion (of the trajectory in fact) of a particle over the surface of a cylinder.Homework Equations Lagrangian and Euler-Lagrange's equations.The Attempt at a Solution I've found the Lagrangian of the particle to be...
  37. J

    Calculating Graphite Quantities: Formulas and Methods Explained

    Homework Statement I need to solve a task which requires to calculate the quantities of graphite. For instance, the particle amount per emission. I think my calculation may use the wrong method/ formula, but I do not know alternative right equation. The data available: graphite granularity...
  38. F

    Mining Large Quantities of Data (~250 million vectors)

    Homework Statement I am given the first human chromosome as a long list of bases: ATGCCTGC... (I have N bases) I have to divide the the chromosome into subsequences of length L, so subsequences are as follows: From base 1 to base L From base 2 to base L+1 From base 3 to base L+2 ... From base...
  39. T

    Optics problem, adding quantities

    Homework Statement -Find the sum of the two quantities: Y1=sin(Wt) Y2=sin(Wt+30 degrees) Homework Equations Y(x,t)=AsinK(kx+Wt) <------- not sure if this is relevant W=2(3.14)f , where f=frequency The Attempt at a Solution sin(Wt) + sin(Wt+30) = sin(Wt) + sin(Wt) +...
  40. ShayanJ

    Invariant Quantities in SR: Explained

    I'm really confused about invariant quantities.Could someone explain which quantities are invariant in special relativity and how are they recognised? thanks
  41. C

    Which quantities are naturally forms, and which are (multi)vectors?

    Which quantities are "naturally" forms, and which are (multi)vectors? I'm undertaking a self-study of geometric algebra and differential forms. It is very enlightening, but I find I'm getting a bit confused by which kind of beast is most "natural" for a particular physical quantity. Where...
  42. A

    Why global conservation of certain physical quantities is not enough?

    What is the implication of the fact that quantities like electric charge, color etc are conserved not just globally but in local region of space too? I understand the later is more restrictive but what advantage does it offer?
  43. N

    Conserved quantities in the Feynman diagrams.

    I'm currently reading Griffiths book (I'm at chapter 4) on Particle physics, and I had a question about Feynman diagrams. In every "node" of a Feynman diagram, what quantities are conserved? Further, what quantities are conserved over the entire diagram?
  44. rpt

    Are space and time quantized quantities?

    Does assuming time and space are quantized quantities make predictions of quantum physics more accurate? I have heard about the "Planks time" but do not know whether its is really a concept in quantum theories.
  45. N

    Common derived units of the physical quantities

    Hi all! I came across 2 questions on my course work, and i don't know what is required here, can some one help please? Q.1 Define the common derived units of the following physical quantities; and express them in terms of the base units: Mass, Length, Time and Electric charge (or Electric...
  46. M

    Effect of adding two per share quantities

    Hi, Please see the attached document. In a simple calculation, I am trying to add the cash flow per share of two companies. I think I am doing something wrong as I am not able to reconcile the results of this calculation to the actual results. Can you please take a look? Thanks, MG.
  47. D

    Is the Boltzmann Equation in GR Truly Coordinate Independent?

    Hi everyone, have a question about covariant, coordinate independent quantities in GR. Reading Kolb and Turner's book The Early Universe one can find the Boltzmann equation in a GR setting. Now, one of the terms in that equation is - \Gamma_{\alpha \beta}^\gamma p^\alpha p^\beta...
  48. D

    Projectile Motion (Vector Quantities)

    Homework Statement A golfer rips a tee shot from an elevated driving range tee-off such that the ball leaves horizontally. The ball lands exactly at the 66.8 meter marker, and was shot from the upper level (6.5 meters above the ground). How long was the ball in the air? And how fast did...
  49. D

    Projectile Motion (Vector Quantities)

    Homework Statement Determine whether each statement below is True or False. 1. T/F Single vectors may be represented as pairs of vector components. 2. T/F Vector quantities are completely described by magnitude only. 3. T/F A scalar quantity requires both magnitude and direction for a...
  50. 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...
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