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. ChrisVer

    Running Constants: Unifying Gaugino Masses in SUSY

    Well I am having some difficulty in understanding the running constants... I am not sure if this applies to the Standard Model as well, but I saw that in SUSY recently... If we take the value of the gaugino masses m_{\bar{g}},m_{\bar{W}},m_{\bar{B}} (by bar I mean Gluino,W-ino and B-ino) to be...
  2. carllacan

    Alternative definition of constants

    Hi. First off, sorry about the title, its not very descriptive but I had no clue on how to sum my question. I'm reading Sakurais' Modern Quantum Mechanics. In the discussion of the K operators (p47) he compares it to the classical momentum operator, states that K = p/(some constant) , and...
  3. F

    A question about fundamental constants in Multiverse idea

    Has there been a debate as to whether fundamental constants can be chosen freely for a theory or some constraints make it unlikely that to be the case. for example the dimentionful parameters don't have a specific value, only combinations give FSC, that means(to my mind) that there is unlikely...
  4. ETBunce

    MHB Non-linear function with two unknown constants and one variable

    Am am presented with the problem: h(t) = c - (d - 4t)^2 At time t = 0, a ball was thrown upward from an initial height of 6 feet. Until the ball hit the ground, its height, in feet, after t seconds was given by the function h above, in which c and d are positive constants. If the ball reached...
  5. T

    After two time constants of time have elapsed, the current in the circ

    After two time constants of time have elapsed, the current in the circuit is how many times the final current?
  6. E

    Engineering RC circuit time constants and coefficients

    Homework Statement I have got this circuit: I have to find coefficients k1 and k2, and time constants T1 and T2. Actually, we can see that T1 =R1*C1 and T2=R2*C2, but is it possible in this circuit or it's just theoretically time constants? I'm not sure, but as there is no amplifier in...
  7. J

    Time, energy, information constants

    hello, I'm not a physicist, just a goofy gent with some far fetched ideas is it safe to say that all the energy and matter in the universe has been constant since big bang? would it be ok to assume that all the time and information has also been constant since the big bang? Been...
  8. B

    MHB Eliminating constants in a second derivative of a function

    Eliminate the constants $y=c_1 e^{ax}cosbx +c_2e^{ax}sinbx$ since there's two constants I took the derivative twice $y'=c_1\left ( -e^{ax}b\sin{bx} + ae^{ax}\cos{bx}\right )+ c_2\left ( e^{ax}b\cos{bx} +ae^{ax}\sin{bx}\right )$ $y''=c_1\left [ \left (...
  9. S

    Find constants of function with given conditions

    Homework Statement Let ##a>0## and y(x)=\left\{\begin{matrix} -x ;& x<-a\\ Cx^2+D;& -a<x<a\\ x;& x>a \end{matrix}\right. a) Find ##C## and ##D## so that ##y\in C^1(\mathbb{R})## b) For A>a calculate ##\int_{-A}^{A}(1-({y}')^2)dx## c) Is it possible to find ##C## and ##D## so that ##y\in...
  10. P

    MHB Constants & Limits: Integration & Anti-Derivative Q

    So I have this question: And I just want to check my answer. Am I right? I think that the first formula is the theorem of integration so a and b are limits o integration and I'm not sure about the second formula, I think it's the anti derivative formula making that the anti derivative...
  11. 9

    Finding Derivatives with Constants

    Homework Statement Let μ represent a positive constant. Find the derivatives of: (x^2)/(2μ) Please check work. I am confused about the "constant" part. Can't you just set μ = some positive number and find the derivative that way? Homework Equations (x^2)/(2μ) The Attempt at a Solution...
  12. B

    MHB Elimination of arbitrary constants 2

    eliminate the arbitrary constant, 1. $\displaystyle y=mx+\frac{h}{m}$ h is a parameter, m to be eliminated.2. $cxy+c^2x+4=0$ eliminate c I don't know where to start please help me get started. thanks!
  13. B

    MHB Elimination of arbitrary constants.

    1. eliminate B and $\alpha$ from the relation $\displaystyle x=B cos(\omega+\alpha)$ in which $\omega$ is a parameter(not to be eliminated). I first took the two derivatives of x with respect to t: $\displaystyle \frac{dx}{dt}=-\omega B\sin(\omega+\alpha)$ $\displaystyle...
  14. I

    Solid state physics, lattice constants, ionic radii, nacl

    Homework Statement NaCl (a0 = 5.64A° ), NaBr (a0 = 5.98A° ) and KCl (a0 = 6.30A° ) all have the same structure, which is the NaCl structure. (a) Assuming the spacings are determined by the ionic radii of the relevant ions, what would value would you expect for the lattice constant of...
  15. K

    Charge after three time constants?

    Homework Statement A 10V supple is connected to a 2.2μF capacitor in series with a 10kΩ resistor. To what value will it have charged after three time constants? Homework Equations I know that T=RC but I have no idea beyond this point The Attempt at a Solution T=RC T=2.2μF*10kΩ...
  16. I

    Fixing the Constants of Equations to Unity

    So I was revising elementary classical physics and Newton's equations of motion. When you apply a force on an object in free space, far from gravitational fields, you find that the object accelerates. By conducting experiments where you vary the force or the mass and look at the acceleration...
  17. R

    Schrodinger Equation in Spherical co-ordinates. Constants.

    When normalising the S.E. in spherical coordinates you split it up into 3 integrals, with respect to r, theta and phi. My question is, once you have found the constants for each, when writing out the normalised PSI do you simply place them as a product in the solution? i..e PSI...
  18. TheDemx27

    How are One-Dimensional Numbers Useful (Coupling Constants)

    How would it make any sense to use dimensionless numbers to represent physical things? From wikipedia: If you are comparing the strength of forces, and you are using these numbers to do so, I would have thought that these numbers would represent units of - well, force. Clearly I must...
  19. Crazymechanic

    Big bang , physical constants , possibilities

    Hello , so the question is basically like that , I did some thinking about evolution and so I came to this question. Now the universe today with it's proton size and mass and particle charges , gravitational constant and all other things we know and yet don't know about , seems kinda precise...
  20. N

    Can Constants with Variables Cancel Out to Create a Constant?

    Homework Statement if a value has a variables that cancel out can it be considered a constant? looking to make an equation out of proportionality statements Homework Equations this is the equation that we are supposed to get: f=√((F)/(4∏2mr)) the 3 proportionality where f2=kF ...
  21. DreamWeaver

    MHB Series acceleration formulae for common transcendental constants

    OK, so for starters, I'm not asking anyone to re-post results found in other books, papers, etc. That'd be entirely contrary to the basic idea of this 'ere thread. What I'm really interested in is this: have you - yes YOU, personally - found any new or presumably unique series acceleration...
  22. F

    Spring Constants and Conservation?

    Spring Constants and Conservation?? Homework Statement In the dangerous “sport” of bungee-jumping, a daring student jumps from a balloon with a specially designed elastic cord attached to his waist. The unstretched length of the cord is 22.2 m, the student weighs 326 N, and the balloon is...
  23. S

    Engineering Determining Constants in Second Order Circuit Analysis

    Homework Statement This was an electrical engineering lab, dealing with the steady state response of an RLC circuit (diagram attached). The main part of the lab consisted of experimentally determining the circuit's critical resistance value, and viewing the overdamped and underdamped...
  24. Primroses

    Structure constants in Lie algebra

    I am studying QFT and got stuck on one question which may be simple. Why is structure constants (in Lie algebra) real and independent on representations? Can you give me a detailed proof? Thanks!
  25. K

    Constants of Nature (and SM Parameters)

    I'm reading Peter Woit book "Not Even Wrong" and have been contemplating on the constants of nature or the parameters. I have some questions. 1. Which of the Constants of Nature do you think can be calculated by principles? Should they in principle be calculable? 2. Should a Unified...
  26. F

    MHB IVP find constants to solution

    The given family of functions is the general solution of the D.E. on the indicated interval. Find a member of the family that is a solution of the initial-value problem. y=c_1x+c_2x\ln{x} on (0, \infty) and x^2y''-xy'+y=0 and y(1)=3, y'(1)=-1 So plugging in y(1)=3 gives 3=c_1+c_2\ln{1} and...
  27. O

    Forced Oscillator with unfamiliar forcing function and constants

    Homework Statement A force Fext(t)=F0[1-e(-a*t)] acts, for time t>0, on an oscillator which is at rest at x=0 at time 0. The mass is m; the spring constant is k; and the damping force id -b dx/dt. The parameters satisfy these relations: b=mq and k=4mq2 where q is a constant with units...
  28. F

    MHB Initial value problem with lots of constants

    L \frac{di}{dt}+Ri=E and we're given i(0)=i_o I,R,E,i_o are constants. So I rewrite equation as \frac{di}{dt}+\frac{R}{L}i=\frac{E}{L} therefore P(i)=\frac{R}{L} let \mu(x)=e^{\int \frac{R}{L}dt}=e^{\frac{tr}{L}+C} multiply equation by integrating factor to get e^{\frac{tR}{L}}...
  29. P

    Smallest set of fundamental physical constants?

    Hi, everyone. I once saw a science program with the danish astrophycisist Jens Martin Knudsen, who said that there exists seven absolutely fundamental constants of nature, and if one of these were changed ever so slightly, it would lead to drastic changes in the whole universe. So my...
  30. C

    Finding the constants in an Electric Field Equation

    Homework Statement The problem calls for finding the relationship between the constants A and B in the following equation of an instantaneous electric field: E=[A(x+y)\widehat{a}_{x}+B(x-y)\widehat{a}_{y}]cos(wt) The details of the medium in which the field exists are that it is...
  31. shounakbhatta

    Planck's Unit and universal constants

    Hello, I am reading Planck's Unit. What I understand is that what is the need for Planck's unit. Kilogram, meter and second are measurement, rather arbitrary measurement, which humans have done in the past. The question is what do we know that is constant throught the universe? We know (1)...
  32. PsychonautQQ

    Deriving of the constants in Fourier Analysis

    Homework Statement Wow LaTex fail... anyone know how i make this look like not ****? I had it looking all pretty on http://www.codecogs.com/latex/eqneditor.php and it gave me these codes as my latex markup but it didn't come out right... why do they look like source code and not the pretty...
  33. K

    Coupling constants, units and measurements

    I was thinking about units and started wondering about coupling constants. In unit-independent form, the fine-structure constant is defined as \alpha = \frac{k_e e^2}{\hbar c} I don't have a deep knowledge of particle physics but I know that there are weak and strong charges which enter the...
  34. B

    Differential Equations-Finding Constants

    Differential Equations--Finding Constants Homework Statement I uploaded a pdf document, which contains the problem I am currently working on, namely, problem number 7Homework Equations The Attempt at a Solution I am having particular difficulty with this portion of the solution: "(ii) At y=3...
  35. B

    Finding The Constants a,b and c.

    Homework Statement In Exercises 49 and 50, find values of a, b, and c(if possible) such that the system of linear equations has (a) a unique solution, (b) no solution, and (c) an infinite number of solutions. 49. x+y ~ = 2 ~y+z =2 x+ ~ z =2 ax + by + cz=0 Homework Equations...
  36. D

    MHB Question on solving system of equations with constants....

    It's fairly straight forward to find information on how to solve a system of equations like this: 2x + 3y + 4z = 1 3x + 4y + 3z = 2 4x + 5y + 3z = 3 It has numerical constants in front of each term. You could use Gaussian elimination and solve for one, infinite, or no solutions. (The above...
  37. R

    Clarification needed: u-sub requires combining 2 constants

    Homework Statement Evaluate ∫-x/(x+1) dxHomework Equations The Attempt at a Solution I do a U-sub u=x+1 du=dx x=u-1 -∫(u-1)/u du -∫[u/u - 1/u] du -∫1 - 1/u du -[∫1du - ∫1\u du] -[u - ln(u) + C] ln(u)-u+C ln(x+1)-(x+1)+C ln(x+1)-x-1+C I combine -1 and C into a single C to get the...
  38. T

    Is it possible that nature laws constants changed over time

    I am wondering ? is it possible that the constants that govern the laws of physics was different during other periods of our universe history ?
  39. U

    Calculating Energies of Pion - Seeming trouble with constants?

    Homework Statement Calculate the energy for 1S->2P transition in lithium and carbon. We had to calculate the energy and eigenvalue equations (though I verified these are correct) Homework Equations E = mc^2/sqrt(1+(Za/lambda)^2) lambda = n + 1/2 + sqrt((l+1/2)^2- (Za)^2) The...
  40. S

    EFT & change or coupling constants

    I understand that by uncertainty relations, it is possible use an EFT to a range of energy, forgotten the interactions for bigger energies. But, ¿ why change the values of coupling costants? And, ¿ how can tell that there is no intermediate particle that happens with low probability in...
  41. F

    Equation linking all fundamental constants

    Folks, I remember once seeing an equation that linked all the important fundamental constants - electron charge/alpha, gravitational constant, planks constant, speed of light, electron mass etc - in a dimensionless relationship. But for the life of me I cannot find it -google doesn't know...
  42. B

    MHB Find the constants given the domain and range

    Suppose you have a function y = f(x) such that the domain of f(x) is 1 ≤ x ≤ 6 and the range of f(x) is −3 ≤ y ≤ 5. a) Find constants B and C so that the domain of f(B(x − C)) is 8 ≤ x ≤ 9 B= C= b) Find constants A and D so that the range of Af(x) + D is 0 ≤ y ≤ 1 A= D= I'm working on...
  43. C

    Measuring effective (renormalized) coupling constants

    How is the effective (or renormalized) coupling constant at a given momentum scale scale measured? If one wants a definition which makes it easy to measure I would think it would be natural to use the LSZ formula which connects the measurable Feynman amplitude with the amputated greens...
  44. Y

    How many time constants must elapse in a capacitor?

    Homework Statement How many time constants must elapse if an initially charged capacitor is to discharge 55% of its stored energy through a resistor? Homework Equations The Attempt at a Solution I don't even know where to start, so please a nudge in the right direction would help...
  45. S

    Deriving Oort Constants From Kepler's Third Law

    Hello everybody. New here. Hope you are all doing well. I am a sophomore in college, studying physics and astronomy. I am in my first astrophysics class and struggling with how to approach problems. That being said, I need a little homework help if you can afford some time! 1. Starting with...
  46. J

    Gas impingement flux, problem in substituting constants

    Homework Statement gas impingement flux density is given by ∅=P/\sqrt{}2mkT where m- mass of a molecule show that ∅=3.513*1022P/\sqrt{}MT where pressure in torr and M-molar mass of molecule then ∅ in molecules per cm2 per second Homework Equations ∅=3.513*1022P/\sqrt{}MT...
  47. N

    Spring Constants, Work, and Force

    Homework Statement Suppose for some unexplained reason you are skateboarding and wanted to use a spring to launch you off a ramp. Assuming you have a mass of 70 kg, if the spring has a spring constant k = 625N/m and is compresed 5m. 1.If the ramp has a 60° and is 10m long, will you make it...
  48. K

    Engineering RC Circuits and Time Constants

    Homework Statement For the circuit below, the switch has been closed for a period of time long enough for steady state conditions to have been reached. a: Determine the time constant before the switch is opened b: Determine the time constant after the switch is closed c: Determine the...
  49. M

    Find units of rate constants and write reactions

    Homework Statement Find the units of k1, k2, k3, k4, and k5. Write rate reactions for dA/dt a. A\leftrightarrowB k1 (forward) k2 (backward) b. A + B \rightarrow C k3 (forward) c. A + R \rightarrow 2R k4 (forward) d. A \rightarrow B k5 (forward) Homework Equations...
  50. Safinaz

    What are the SU(3) structure constants and how can they be calculated?

    Hi, How can I calculate such terms d^Aae d^ebD f^AaE f^EbD d^Aae d^EbD f^AaE f^ebD Cheers, Safinaz
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