What is Constants: Definition and 486 Discussions

A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, which has a fixed numerical value, but does not directly involve any physical measurement.
There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c, the gravitational constant G, the Planck constant h, the electric constant ε0, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed for any object and its dimension is length divided by time; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.
The term fundamental physical constant is sometimes used to refer to universal-but-dimensioned physical constants such as those mentioned above. Increasingly, however, physicists only use fundamental physical constant for dimensionless physical constants, such as the fine-structure constant α.
Physical constant, as discussed here, should not be confused with other quantities called "constants", which are assumed to be constant in a given context without being fundamental, such as the "time constant" characteristic of a given system, or material constants (e.g., Madelung constant, electrical resistivity, and heat capacity).
Since May 2019, all of the SI base units have been defined in terms of physical constants. As a result, five constants: the speed of light in vacuum, c; the Planck constant, h; the elementary charge, e; the Avogadro constant, NA; and the Boltzmann constant, kB, have known exact numerical values when expressed in SI units. The first three of these constants are fundamental constants, whereas NA and kB are of a technical nature only: they do not describe any property of the universe, but instead only give a proportionality factor for defining the units used with large numbers of atomic-scale entities.

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  1. Y

    Mathematica How to define local variables and constants in mathematica

    hi suppose i run Two notebook and in each of them i have matrix A and Constant B and a function C in each notebook these things have the same name. if in notebook 1 i assign B=10 then in notebook 2 B is 10 too , which is not my desire. how can i define these constants and matrices and...
  2. J

    E&M: Find relationship of the constants for a given magnetic field

    Homework Statement Given the magnetic field B= α*x*y x^ + β*y^2 y^. What is the relationship between α and β. Find the current density J. Homework Equations I know that the relevant equations are Δ dot B = 0, Δ x B = μJ, Δ dot A = 0, Δ x A = B The Attempt at a Solution I know...
  3. M

    All The Stuff We Do with Equilibrium Constants

    NONE OF IT MAKES ANY SENSE! For example: If we divide the molar coefficients all by 2, then we raise the original equilibrium constant by the same power (0.5). If we write the reaction in the reverse, then the new equilibrium constant is the multiplicative inverse of the original...
  4. jfy4

    Structure constants to metric

    Hi, Let's say I have a 10 dimensional Lie algebra over some field of functions, something along the lines of at least twice differentiable with twice differentiable inverses. The structure constants have inputs from this field. Is it possible to build a metric from these structure...
  5. R

    Using Partial Derivatives to check B-S Equation holds and find constants

    The question I'm trying to solve is part (ii) of the attached file I've used partial derivatives to input back into the Black Scholes equations and after factorising it, I've got it down to: (a + 2bt + αt +r) * (S².c.e^(at+bt²) = 0 I'm now stuck on what to do next, as there would need to be...
  6. B

    Prove that transversly isotropic materials have 5 independant elastic constants

    Homework Statement So I need to prove that transversly isotropic materials have 5 independent elastic constants. I can prove that an orthotropic material has 9 independent elastic constants. I need to use the transformation matrix to show that some of the 9 mentioned components are equal for...
  7. 1

    Need help finding some unknown constants

    Homework Statement I have an integral that I'm trying to split into partial fractions, and I've gotten to an equation but I'm not sure how to solve this one. Homework Equations The Attempt at a Solution 93x+2 = Ax^2 + Bx + A - 4B I have no idea, because I usually don't have a...
  8. R

    Rayleigh-Ritz Approximation (Obtaining the constants)

    Homework Statement Consider the differential equation -\frac{d^2u}{dx^2}=cos\pi x for 0<x<1 subject to the boundary condition u(0)=0, u(1)=0 Determine a three-parameter solution, with trigonometric functions the least-squares method Given: u=\phi_0 + c_1\phi_1 + c_2\phi_2 +...
  9. C

    One dimensional medium with 2 different dielectric constants

    I just got this question on a classical mechanics assignment... and unfortunately I know NOTHING about dielectric materials (never been introduced to me for some reason >.<). I don't even know why this is on my classical mechanics assignment but it is anyway. And btw there is a disclaimer on the...
  10. Z

    Evaluating double integrals for bending-torsion coupling constants

    I've been trying to compute the bending-torsion coupling constants for a wing, B1, B2 and B3. The expression for this is \begin{bmatrix} B_1 \\ B_2 \\ B_3 \end{bmatrix} = \iint (y^2 + z^2)\begin{bmatrix} y^2 + z^2 \\ z \\ y \end{bmatrix}dydyz where x is in along the wingspan direction, y...
  11. R

    What are the values of a and b in this vector equation?

    Let a\vec{A}+ b\vec{B} + \vec{C} = 0, where \vec{A} = (75, -60), \vec{B} = (-16, 60), and \vec{C} = (84,16). I need to find the value of a and b. I really have no idea where to start with this problem any help would be great!
  12. tom.stoer

    Covariant global constants of motion in GR?

    We know that in GR it is not possible for arbitrary spacetimes to define a conserved energy by using a 3-integral. There are some obstacles like the covariant conservation law DT = 0 (D = covariant derivative; T = energy-momentum-tensor) does not allow for the usual dV integration (like dj...
  13. teroenza

    One variable equal to two constants = inconststant?

    Homework Statement I have been given a 3X4 matrix and asked to find whether the plane equations which are it's constituents intersect at least at a single point. I end up with one variable equal to two different constants. Is this an example of inconsistency, and thus the planes to not...
  14. T

    Beam Theory Constants Question

    From my understanding, the equation that models the transverse vibration of a beam is (Euler Bernoulli): u_{tt} = - \frac{EI}{A \rho} \cdot u_{xxxx} where E is Young's modulus, I is the 2nd moment of area, A is the cross-sectional area, and rho is the density of the beam. This equation...
  15. J

    Integration of a Square Root including constants

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  16. M

    Can the Time Constant Explain the Behavior of RL Circuits?

    Hello, I am currently studying RL circuits and I know that when an inductor is attached to a resistor of large value, the time for the energy stored in the inductor to dissipate in the resistor is shorter and vice versa. This is proven mathematically by the time constant term Tau : L/R But...
  17. K

    Mathematica Plotting arbitrary constants in mathematica

    How do you plot arbitrary constants in mathematica? for example r(psi)=a(1-eCos(psi)), where a and e are some constant. Thanks in advance for the help.
  18. F

    Calculating Net PE in Ions: A & B Constants

    The general expression for calculating net potential energy in ion is: PE (r) = A r^m + B r^n where A & B are proportionality constants. What exactly are these constants?? Could anyone point me to correct resources?? I'm new at this forum and very interested in learning physics.?
  19. G

    Solve, floor(x/B)+1=L, for x, where B & L are constants & is a variable?

    Solve, floor(x/B)+1=L, for x, where B & L are constants & is a variable? Homework Statement I'm trying to solve this for x floor(x/B)+1=L where x is a variable B and L are just some constants Homework Equations The Attempt at a Solution I have no idea were to go after this floor(x/B)=L-1 I...
  20. L

    DLVO interaction: Choice of Hamaker constants

    For a project, I'm trying to describe the interaction energy between two particles suspended in water which contains ions. I seem to have the double layer effect worked out pretty well, but I'm having trouble with the Van der Waals contribution, or more specifically, with the choice of Hamaker...
  21. A

    Spring Constants and compression

    Homework Statement A 5.0kg mass is hanging from a spring scale and is slowly lowered onto a vertical spring. The scale reads in Newtons. a) what does the scale read when the mass is not in contact with the spring? b)the scale reads 20N when the lower spring is compressed by 2.0cm. show...
  22. A

    Solve Spring Constant: 40g Mass, 20N/m

    Homework Statement A mass of 40.0 grams is attached to a vertical spring with a spring constant k = 20.0 N/m and lowered slowly until the spring stops stretching. How much is the spring stretched? The Attempt at a Solution I assume I have to use F = -kx? But I don't know the force so...
  23. G

    Does the Compressibility Factor of a Gas Relate to Van der Waals Constants?

    Does the compressibility factor of a gas say anything about Van der Waals constants?
  24. J

    Additivity of Time Constants in Series RC Circuits

    Does anyone know of any instance where the the time constants of two RC circuits in series is additive. It seems that when R1=R2 and tao1~tao2 this holds?
  25. J

    Expressed in terms of the constants

    Homework Statement "Expressed in terms of the constants in this model, how high is the lowest point of the cable? (Assume the correct dimension to be in metres)"Homework Equations Equation for the shape of a hanging cable. [PLAIN]http://img59.imageshack.us/img59/8672/eqn6142.png edit: P, g...
  26. C

    Find (practical) current source constants, I and R

    Homework Statement A practical current source has a current of 22 A. Loading the source with 50 \Omega results in terminal voltage of 390.3 V. Obtain the source constants, I and R.Homework Equations V=I\times RThe Attempt at a Solution In my clumsy picture below, shouldn't I_{load} be replaced...
  27. F

    How is the quotient of two constants calculated in a given equation?

    Homework Statement Part of a larger problem. I know that F_{1}^2+2F_{1}F_{2}-F_{2}^2=0 where F_{1} and F_{2} are x and y components of a force. Hence \frac{F_{1}}{F_{2}}=1\pm\sqrt{2} I can't see how that step is done. Homework Equations The Attempt at a Solution...
  28. R

    Inflaton Field, Cosmological Constants and Spacetime

    I can accept that spacetime has no substantial aspect to it because for General Covariance (Diffeomorphism Invariance) to be true, spacetime "points" can't be real or else General Covariance won't work. Now question. How does Inflaton Field and the Cosmological Constants for example interact...
  29. G

    Calculating Distance Using Spring Constants: 20-Minute Crash Course

    Calculating distance using spring constant, mass and velocity? (Really basic stuff!) Hi I have a physics exam tomorrow, and I just realized we haven't covered either impulse or spring constants, and about 1 1/2 hours left to study. From a practice exam, please someone help me out? Homework...
  30. E

    LSZ reduction and Renormalization constants

    Hey folks, i have a question about LSZ and how to take into account the renormalization constants of the theory in question. In the derivation, only the field strength renormalization enters as a factor of Z (or square root thereof) but some mates said that also the vertex renormalization...
  31. F

    RC circuit problem with time constants

    Homework Statement http://img193.imageshack.us/img193/3696/aasdff.th.png Uploaded with ImageShack.us The Attempt at a Solution (a) No current, so no time constant since C = 0 for it stores no charge (b) Current immediately is driven through so \tau = (R_{1}+R_{2})C (c) I pulled the...
  32. B

    Renormalisation constants in QED

    Hi, I have been deriving the renormalisation constants in QED as part of my project. I have been using Peskin and Schroeder. I am a bit confused with a couple of things and was wondering if anyone could please help! Firstly, why do we chose not to absorb the Z_3 constant in the electron...
  33. H

    Finding three Constants given only relative Max, and y intercept

    Homework Statement Find constants a, b, and c such that the graph of f(x) = ax2 + bx + c has a relative maximum at (5 , 12) and crosses the the y - axis at (0 , 3). Homework Equations Not sure what to use The Attempt at a Solution -- i don't have one --
  34. Saladsamurai

    Power Series: Question about constants

    Homework Statement So I have attached the problem in image: Pr and A are just numbers (constants) that are given. I solved the equation by power series solution. However, I am just confused because it is a second order DE but I only have one arbitrary constant of integration ao. I am not...
  35. R

    Small change in constants, big change in integral

    Check this out, 1/(x2+a) where "a" is a constant When this function is integrated, if a is positive then we get something like arctan of something, if a is 0 we simply get -1/x, and if a is negative then we get something involving the natural logarithm, and yet there's something very similar...
  36. C

    Power delivered by Battery to Capacitor in Time Constants

    Power delivered by Battery to Capacitor in "Time Constants" Homework Statement < Pic 1 > The Attempt at a Solution < Pic 2 > As you see, I'm getting answer as (ln 2)/2 but the answer is just (ln 2) Please tell me where I'm wrong.
  37. J

    Looking for particular Diatomic Molecular Constants

    Hello, I've been looking for a few rotational/vibrational diatomic molecular constants for N2 and O2. I've got a some good literature values for most constants I need involving the calculation in possible vibrational and rotational energy states. I'm looking for the centrifugal distortion...
  38. D

    Constants of nature as determined by string theory

    Hi all, I remember in the Elegant Universe (the documentary), at some point the following lines were said: "So what exactly, in nature, sets the values of these 20 constants so precisely? Well the answer could be the extra dimensions in string theory. That is, the tiny, curled up...
  39. P

    Making three equations orthonormal by forcing the constants

    [b]1. Make these three equations orthonormal to each other in the interval 1 less than or equal to x greater than or equal to 1 (this may be a typo as I think it should read 1 less than or equal to x less than or equal to one) by determining the appropriate values for the coefficients a b c d e...
  40. N

    Thermodymanics dealing with pressure, temperauture, and constants

    Homework Statement A bubble of air, 0.010m^3 in volume , is formed at the bottom of a lake which is 30m deep and where the temoperature is 8 degrees c. The bubble risees to the surface, where the water temp is 26 deg c and where the pressure is atmospheric pressure. What is the volume of the...
  41. T

    Natural constants: are they irrational numbers?

    Do we have at present any knowledge whether our natural constants (gravity constant, Planck's constant, ...) are rational or irrational numbers? Thanks, Trinitiet
  42. R

    Calculate Spring Constants: 0.400 and 0.225 Joules

    Can someone please just explain to me how to do this? I feel helpless. A spring has a force of 500.0 N/m. Show that the potential energy stored in the spring is as follows: a.) 0.400 Joules when the spring is stretched 4.00cm from equilibrium. b.) 0.225 Joules when the spring is...
  43. B

    Why are there different rate constants?

    Hey, The decomposition of A is first order, and [A] is monitored. The following data are recorded: t / min 0 1 2 4 [A]/[M] 0.100 0.0905 0.0819 0.0670 Calculate k. Using [A] = [A]0e-kt, Calculating at t = 1 0.0905 = 0.1e-k(1) 0.905 = e-k -0.0998=-k k =...
  44. G

    Can You Choose Your Own Constants in Differential Equations Integration?

    On this page below, the person chooses the constants to be anything they want, but can you actually do that? Pauls Online Notes : Differential Equations - Reduction of Order
  45. R

    Finding the constants in a general solution

    I have x(t) = C(sub1) sin(16t) + C(sub2) cos(16t) Given: initial position x(0) = 1/6 so: 1/6 = C(sub1) sin(0) + C(sub2) cos(0) 1/6 = C(sub2) but how do i find C(sub1)? I am not given initial velocity
  46. Q

    Can you find two different constants by Noether's theorem

    Homework Statement Consider a 3-dimensional one-particle system whose potential energy in cylindrical polar coordinates \rho, \theta, z is of the form V(\rho, k\theta+z), where k is a constant. Homework Equations The Attempt at a Solution I already find a symmetric transformation: \rho...
  47. E

    Miniscule changes in the physical constants?

    I have been reading that observations of distant quasars over the past decade have been suggesting that there have been minuscule changes in our physical constants. An estimate was given about 1 part per 100000 every billion years. If such a change is indeed happening, then it is safe to assume...
  48. T

    Relationship between Kt and Km constants in a motor?

    I know how to measure Km, but I already know Kt from the datasheet and according to some motor calculation guide's I've found online, they say you can know one from the other by using the relationship: Kt (oz.-in) = 1.345 * Km (V/1000 rpm) I checked this on other motor's datasheets that give...
  49. C

    Calculating Group Constants for FA with MCNP

    hi there I wnat to calculate the group constants for a FA(fuel assembly) using MCNP (similar to lattice calculations). How can I do it? Please lead me. Thanks alot!
  50. J

    Derivatives of a Constant in a Trigonometric Function

    Homework Statement Find y'' if y=1/3(1+cos^2(√x)) Homework Equations The Attempt at a Solution Now I believe I got the first derivative right since the teacher marked ir right, but my real question here is what do I do with the 1/3? Is it ok to throw away the constant when I...
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