Constants Definition and 486 Threads

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. astroman707

    If given A,B,C, Find constants x,y |xA +yB=C

    Homework Statement Three vectors are given: A=2i+3j, B=1i+5j, C=-1i+3j Find constants x and y such that xA+yB=C Homework Equations N/A The Attempt at a Solution The form of the final equation reminded me if standard form of a slope, so I found the total vector for A,B, and C. I was then going...
  2. A

    I Finding the constants in an expression

    I have a problem with this formula: I have two known value series: A1, B1, C1 and A2, B2, C2. That gives me two equations with two unknowns n and k. Mentor note: More readable versions of the two equations: $$A_1 = \sqrt[n]{\frac{B_1} k + C_1^n}$$ and $$A_2 = \sqrt[n]{\frac{B_2} k +...
  3. D

    After how many time constants is capacitor energy 1/4?

    Homework Statement [/B] After how many time constants is the stored energy of a discharged capacitor one-fourth its initial value? Homework Equations [/B] (1) U = Q2/2C (2) U = Qmaxε/2 (3) q(t) = Qie-t/RC The Attempt at a Solution The solution can be correctly attained using the first...
  4. John Greger

    Solving for Hyperfine Constants in the 6s-8p Transition of 115In

    Okey so I think this question or a similar one was here recently but I can't find it so creating a new. Homework Statement The figure below shows the hyperfine structure in the transition 6s ##^2S_{1/2} - 8p ^2P_{3/2}## in 115In (I = 9/2). The measurement is made using a narrow-band tunable...
  5. MathematicalPhysicist

    A Given a Metric, find the constants of motion

    I have another question, if I am given a metric and I want to find the constants of motion of that system, then how do I do it? Thanks!
  6. osilmag

    I Exploring Chaos Theory Constants: Beta, Prandtl, and Rayleigh

    One of the constants in chaos theory is symbolically labeled as beta, however I haven't found an official definition. The other constants Prandtl and Rayleigh deal with viscosity and diffusivity so they must be appropriate for the specific situation. Is beta simply a constant that can be changed...
  7. SamRoss

    B Relativistic Energy: Change of Consts. of Integration

    In this super short video of the derivation of the relativistic kinetic energy, , I'm just stuck on one thing. Around 1:00 minute in, the constants of integration change from 0 to pv when the integration changes from dx to dv. Where does the pv come from? Thanks!
  8. S

    Why are the constants a and b independent of temperature in gas properties?

    Homework Statement My book says that the constants a and b are characteristic properties of a gas, and they do not depend on temperature. But i am having trouble understanding it. Homework EquationsThe Attempt at a Solution We know, a = ΔP*V2 / n2 , but volume is temperature dependent, so how...
  9. binbagsss

    Feynman Vertex Rule, Correlator, 2 different coupling constants

    Homework Statement Vertex Feynamnn rule for computing the time correlator of fields under an action such as, for example, Say ##S_{int} [\phi] =\int d^4 x \lambda \frac{\phi^4(x)}{4!} + g \frac{\phi^4(x)}{4!} ##, ##\lambda## and ##g## the coupling constants. Homework Equations see below...
  10. J

    I Where are the Constants of Nature stored in Multiverse?

    In Multiverses where there are different constants of nature such as the mass of the electron or the value of the strong coupling constants. Where are the values stored? If there were no compactified calabi-yau manifolds that produced the values and they were just like that. What maintains the...
  11. PumpkinCougar95

    B Fundamental Constants: How Do We Know They're Constant?

    How do we know that constants in nature like the Gravitational constant or plank's constants are actually "constant" and don't actually change over time? What sorts of experiments have been done which verify these things?
  12. R

    Diff eq with constants... Eulers identity...

    Homework Statement Find the general solution of the second order DE. y'' + 9y = 0 Homework EquationsThe Attempt at a Solution Problem is straight forward I just don't get why my answer is different than the books. So you get m^2 + 9 = 0 m = 3i and m = -3i so the general solution...
  13. slow

    B The values of the fundamental constants

    The reason for initiating this thread is to have read another, initiated by Serra Nova here in the forum, accessible at the following address. https://www.physicsforums.com/threads/fundamental-physical-constants.938267/ The starting note of this thread refers to knowing if those terms called...
  14. Serra Nova

    I Do Fundamental Physical Constants Truly Remain Constant Over Time?

    Why are the fundamental physical constants called "constants" when they change over time? I've read that the constants were adjusted in 1986. How can there even be something that is constant, when we can't even see the entire universe?
  15. pairofstrings

    B What are some commonly used mathematical constants and their purposes?

    Hi. π is a constant. The purpose of π is to use it to find circumference of a circle or area of a circle. Correct? Can you please elaborate? Can you point out any other two constants and its purpose? Thanks.
  16. hilbert2

    A Coupling constants with fractional dimensions

    Most QFT texts, such as Peskin&Schroeder and D. Tong's lecture notes, contain a mention that the renormalizability of an interacting theory requires the coupling constants to have correct dimensions, making scalar fields with ##\phi^5 , \phi^6, \dots## interactions uninteresting. Maybe there are...
  17. T

    I Solving for constants in a differential equation

    I feel so sorry when I found myself trapped in a basic problem like this one, but let's go ahead... Suppose we have the following equation, knowing that ##B## is a constant, $$\frac{dU( \theta)}{d \theta} + 2Br = 0$$ where we want to solve for ##B##. If we differentiate the above equation with...
  18. S

    Calculating 3D Cylinder Volumes & Areas With Constants

    Homework Statement Let r be a positive constant. Consider the cylinder x2 + y2 ≤ r2, and let C be the part of the cylinder that satisfies 0 ≤ z ≤ y. (1) Consider the cross section of C by the plane x = t (−r ≤ t ≤ r), and express its area in terms of r, t. (2) Calculate the volume of C...
  19. S

    Exploring Nature's Constants: Manipulating Variables in the Lab

    If supposed you could locally change any constant of nature in a test area in the lab say the the size of aquarium and you put a marble inside.. could you make the marble bigger and smaller, heavier or lighter by adjusting any of the parameters? or even make the marble explode? What would happen...
  20. D

    Constants of motion in quantum mechanics

    Homework Statement A particle of mass m and spin s, it's subject at next central potential: ## \begin{equation*} V(\mathbf{r})= \begin{cases} 0\text{ r<a}\\ V_0\text{ a<r<b}\\ 0\text{ r>b} \end{cases} \end{equation*} ## Find the constants of motion of the system and the set of...
  21. V

    I Meaning of Constants of Motion in General Relativity

    Hello, I have a mess in interpretation of constants in description of movement in GR. First of all I define Lagrangian ##l=1/2g_{\mu\nu}u^{\mu}u^{\nu}##, and I would like to talk about axial smyetric spacetime (for example Kerr black hole) ##l(r,\theta)##. l is independent from ##t## and...
  22. Beans56

    I Life permitting ranges for fine tuning constants

    Does anyone know What the life permitting ranges for the constants usually mentioned in the Fine Tuning argument are? i.e. h, G, e, rate of expansion, amount of dark matter ect... My thinking is that if they are just kind of randomly placed inside their respective ranges then that would indicate...
  23. jlmccart03

    Find current through inductor after many time constants.

    Homework Statement In the figure, R = 1.9 kΩ and ε0 = 60 V . When the switch is closed, the current through the inductor rises to 10 mA in 30 μs . What will the current in the circuit be after many time constants? Homework Equations I = V/R or I = ε/R if current is constant which after many...
  24. L

    I Dimensionless and dimensioned fundamental constants

    There are 25 or so dimensionless constants in the standard models, such as the masses of the fundamental particles (that can be divided by Planck mass or some other mass to become dimensionless). And there are the three dimensionful constants c, h, G (speed of light, Planck's constant, Newton...
  25. D

    MHB Using constants in expressions.

    import java.util.Scanner; public class ShippingCalculator { public static void main (String [] args) { int shipWeightPounds = 10; int shipCostCents = 0; final int FLAT_FEE_CENTS = 75; shipWeightPound = shipCostCost / shipWeightPound; final int CENTS_PER_POUND...
  26. N

    B Fine Tuning Constants: Understanding Variables and Ratios | Physics NIST

    This isn't a question about whether the universe is fine tuned or not. Which is more of a philosophical issue than a physics one. This is whether anyone on here knows of the variables involved from the following http://physics.nist.gov/cuu/Constants/Table/allascii.txt in the "fine tuning"...
  27. J

    A Can you solve (a-bx)y'+(c-dx)y-e=0 with a,b,c,d,e constants?

    I'm having trouble solving the differential equation (a-bx)y'+(c-dx)y-e=0 with a,b,c,d,e constants. I tried laplace transforming it, but then I end up with yet another differential equation in the laplace domain because of the xy and xy' terms.
  28. saybrook1

    Change of variables and gravity constants

    Homework Statement Hi guys, I'm struggling to figure out how the solution in the picture that I posted was able to get rid of their mg factors and then come up with a factor of k for x_1 in their eigenvalue equation. You can see that in the second equation of motion there is no k*x_1 but it...
  29. A

    Mathematica How to determine arbitrary constants with "Solve?"

    Hi, I am using Solve to solve a system of linear equations with more unknowns than equations. For example, I have 36 variables and Solve returns 30 equations. Six of the variables I can assign a value of one. But I can only figure out which ones are arbitrary by manually looking at the...
  30. vktsn0303

    I Express x in terms of the constants

    I have the expression, A(Bx + 1) = C*d^(2x) where A,B,C and d are constants. How to arrive at an expression for x in terms of A,B,C and d? I have tried doing this: Log [A(Bx + 1)/C] = Log [d^(2x)] 2xLog(d) = Log[A(Bx + 1)/C] but I'm unable to arrive at an explicit expression of x in terms...
  31. K

    B List of Verdet Constants?

    I'm replicating the Faraday Effect as a high school experiment. Can anyone direct me to Verdet constants of water, air, olive oil and table salt for lasers of wavelengths 405nm, 532nm, and 650nm? I'm using the constant as a variable using different materials but I cannot find a specific value...
  32. sounouhid

    Cobalt ferrites Optical constants

    Hi Every one I've been looking ,for a while, for a document that talk about the optical constants of CoFe2O4 witout any results can anyone help me finding one thank you for advance
  33. J

    A Experimental values for screening constants? (Slater rules)

    In multiple-electron atoms the effective charge of nucleus for a given electron, is reduced by the presence of other electrons (including those from more external shells, against the shell theorem): Z_eff = Z - s where the screening constant s depends on Z and the concerning orbital. It is...
  34. physicaled

    Solve Spring Constant Homework Confusion

    Homework Statement The question is "Imagine you are told after performing your experiment that the weights in your weight set are incorrectly labeled, and weigh less than you thought. Does that mean the value you determined for the spring constant is wrong? If so, is your value too high or too...
  35. W

    I Constants of nature in the early universe

    As I understand it, in string theory the constants of nature can taken on a huge different number of possible values and when the universe cools after the big bang these constants of nature get locked in as it were and become , well constants. My question is, what if we discard string theory -...
  36. gaaah

    I Computer exploration of fundemental constants

    Hi, I'm a retired computer programmer (of mostly business applications). I wondered if anyone could tell me if anyone has used programming to investigate the dimensionless physical/mathematical constants in a random way. By random way I mean: write a program to randomly generate an equation...
  37. P

    I Is the author integrating constants?

    Dear Sirs, I am currently calculating a velocity profile of an annular flow. Unfortunatelly I am not understanding the following step: [PLAIN]http://[url=https://postimg.org/image/vl256ffhj/] That seems the author had integrated the R constant. And remains the question: why had R been...
  38. CuriousLearner

    A The physical constants: relationship to mathematics?

    Do we have any examples of physical constants appearing in topics that are focused more on abstract mathematics? For example, do the values of the physical constants ever appear in the results of papers on mathematics that are not focused on direct applications to physics? Could they do so if...
  39. E

    Units of constants in transfer functions?

    Hi All Probably a very basic question. What are the units of the constants in transfer functions? It we take a look at the transfer function of a second order system we then have: H(s) = ω02/(s2+2ζω0s+ω02) ω0 is the natural resonance frequency and has a unit of rad/sec. ζ is the damping...
  40. Battlemage!

    I Permeability/permittivity constants and one way speed of c

    I have heard people argue about an anti-symmetric synchronizing convention allows for a different or even an infinite one-way speed of light. I thought about it and I wanted to know what you thought about the notion that the permeability and permittivity constants completely preclude this notion...
  41. evinda

    MHB Proving the Existence of Constants in a Summation Inequality

    Hello! (Wave) How can we show that there are constants $c_m$ such that: $$\sum_{|a| \leq m} |\xi^a|^2 \leq (1+ |\xi|^2)^m \leq c_m \sum_{|a| \leq m} |\xi^a|^2$$ Could you give me a hint what we could do?
  42. S

    Why Do Force Constants of DCl and HCl Differ by 10 N/m?

    The force (spring) constant of HCl 477.8 N/m, and the force constant of DCl is 487.95. Why should these values differ by 10 N/m? Is a D-Cl bond somehow stronger than an H-Cl bond?
  43. M

    Why can we add/subtract constants to potential function?

    I have 3 questions regarding the topic: 1-Why is that we are allowed to add or subtract a constant to a potential energy function V(x) to set it to zero where it is constant? 2-What does adding/subtracting a constant physically correspond to if anything at all? 3- Do we do it simply for...
  44. M

    MATLAB Need help on constants for Matlab nuke sim for uni project

    Hey guys, I am currently working on a uni MATLAB group project for blast radius, thermal radius etc. Apparently these formula are the best possible to use: r_thermal = Y^0.41 * constant_th r_blast = Y^0.33 * constant_bl r_radiation = Y^0.19 * constant_rad But can anybody tell me what...
  45. H

    I Are physical constants subject to the uncertainty principle?

    Are physical constants, such as the elementary charge or the gravitational constant, subject to Heisenberg uncertainty principle, theoretically and empirically? Theoretically in the sense that infinite precision of these constants will directly violate HUP. Empirically in the sense that, for...
  46. Buzz Bloom

    I Inconsistencies re Astronomical constants

    I have been working on some calculations about the history of our Moon's orbit, and I have found an inconsistency with respect published value for the following four constants: G = Universal Gravitational Constant M = Earth's Mass R = Moon's orbit semi-major axis P = Moon's orbit sidereal...
  47. D

    Interpreting the Constant c in a Savings Account Differential Equation

    Hello! so I'm working on a homework problem where I need to solve the diff equation dy/dt = ky - W where Y is the amount of money in a savings account W is a constant k is another constant (growing at a percentage) solving the diff equation I got y = W(1/k) + ((c)/(e^-kx)) now my question...
  48. J

    Solving Diff Eqns: Renaming Constants & Reversing Signs

    Suppose I'm at this point in solving a differential equation and the initial condition is Q(0) = Q0 -ln|25-Q| + c1 = rt/100 + c2 Then if I combine c2-c1, I can rename it to c, we have: -ln|25-Q| = rt/100 + c Now if I multiply the equation by (-1), I get: ln|25-Q| = -rt/100 - c If I let -c = C...
  49. F

    Can we calculate the coupling constants?

    I know that QFT puts in the coupling constants by hand, based on experiment. And many of the coupling constants are suppose to become equal at the grand unification energy. But I wonder if there is any principle that would allow us to calculate the present day coupling constants based the GUT...
  50. J

    Math of a spiral with two constants

    Homework Statement What type of spiral has constant angular velocity and constant magnitude of velocity? Is there a description of the mathematics that describe the spiral? Homework Equations To be determined. The Attempt at a Solution The closest type I can find is the Archimedean spiral...
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