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. C

    What affects the solubility of CaSO4 in different solvents?

    Say I've got a solid lump of CaSO4 that I put into water. When I first learned about Solubility Constants, Ksp was defined as [Ca][SO4], meaning how much Calcium and Sulfate ions dissolved. But now I found out when I look up a Ksp value it is [Ca][SO4]\gammaCa\gammaSO4. I understand the...
  2. N

    Beat frequency when there are phase constants

    Homework Statement If we have two vibrations with angular frequencies ω1 and ω2 with ω1≈ω2. Then we will have beats with beat frequency ω1-ω2. But suppose we have two different phase constants, for example x1 = Acos(ω1t + ϕ1) and x2 = Acos(ω2t + ϕ2). What happens to the beat frequency...
  3. H

    Detemining the constants in a helix equation (Calculus of Variations question)

    This question is about variable end points in calculus of variations. I understand the basic principle of how you would find the various equations, but I embarrasingly keep getting stuck on when determining the constants. Question: Find the equation of a frictionless wire between the point...
  4. T

    Constants of Motion in the Kuramoto Model

    Hey All, I realize this is a slightly peculiar question - but does anyone know if there is any conserved quantities in the Kuramoto Model. I've been thinking about it, and since the system is made up of coupled Limit Cycle Oscillators and there is no dissipation, wouldn't the total energy be...
  5. P

    Definition of Derivative to Find Constants A, B, and C

    Homework Statement Ax^2 + Bx + C if neg. infinity < x </= 0 f(x) = x^(3/2) cos (1/x) if 0 <x< pos. infinity Use the definition of the derivative to determine all possible values of the constants A, B and C such that f'(0) exists. Cannot use differentiation formulas...
  6. 3

    Solve for constants a and b given the limit of the function

    Homework Statement Determine all the numbers a and b for which the limit of the function as x approaches 2 equals to 4 sorry, I am kinda new at this, not sure how to type it out
  7. F

    Proper handling of witnessing constants in epsilon-delta proofs

    Suppose you had some arbitrary function f : R^n \to R^p and x \in R^n. You want to know if it's continuous, so you do some epsilon-delta to find out for sure. However, only the most simple functions permit this without some extra restrictions. Consider f(x) = x^2. To show that |x - a| < \delta...
  8. X

    Solving for constants given boundary conditions

    Homework Statement http://img843.imageshack.us/img843/3515/11193469.png Homework Equations The Attempt at a Solution [PLAIN][PLAIN]http://img801.imageshack.us/img801/4829/scan0001i.jpg An upload of my attempt to solve the problem. Not sure to interpret the results. A = B...
  9. marcus

    Are congenial constants also holey ?

    Are congenial constants also "holey"? Crowell pointed to two very interesting papers by Jaffe et al and by Jenkins (MIT) This is the long one, with a lot of interesting detail: http://arxiv.org/abs/0809.1647 Quark Masses: an Environmental Impact Statement This other one is more of a quick...
  10. M

    Dielectric constants what is the limit

    Hi there, Do we know which material has the highest dielectric constant (exact figures would be nice),and what is the highest break down voltage achievable for that particular material.
  11. A

    Doubt regarding constants. Elastic Beam Theory.

    Hello. As a good mathematician, I'm having troubles reading some constants for a PDE. I'm modelling an elastic rod using the equation \rho A U_{tt} - N U_{xx} + E I U_{xxxx} = 0, where "\rho is the beam density, A and I are the area and moment of inertia of the beam cross section...
  12. S

    What is the spring constant for a uniformly loaded clamped beam?

    Does anyone know the spring constant for a clamped/fixed beam with length L that is uniformly loaded? I know the spring constant for a clamped beam that is centrally load by a point load is k= 192EI/L^3 I know for a uniformly distributed is different.
  13. G

    Can partial vanishing of Poisson bracket determine local constants of motion?

    I don't know if this is the right place to post this, but my question is: if i have an Hamiltonian defined on the whole phase space and a function f which is also defined on the whole phase space and doesn't depend explicitly on time, i know that if its poisson bracket with the Hamiltonian...
  14. E

    Help with Dielectric Constants

    Hi Everyone, I am trying to find the real and imaginary dielectric constants for TiO2 (rutile) as a function of wavelength. Could anyone suggest a good place to find something like this? Palik has a nice book but it is incomplete, so I'm not sure if there is something newer. Also, could...
  15. R

    How can i obtain optical constants

    can someone trained in ellipsometer can guide me how can i obtain optical constants of a thin film which is sandwiched between two films of known optical constants. with such multilayer samples interference oscillations become difficult to resolve but i am sure that top layer is non-absorbing...
  16. P

    Could a Variable G Explain Dark Energy and Matter in Our Universe?

    What would happen to the universe if the physical constant of Big G was changed?
  17. J

    Orthotropic materials defined by 9 constants

    Could some one explain, or give me a pointer to a good explanation, of how the nine constants that are often used to define orthotropic materials are determined. I understand what E is in each direction. I understand poisson ratio. I sort of understand G. (I understand it as the E...
  18. M

    How Does Hooke's Law Determine Spring Constant and Extension?

    Homework Statement Hooke's law describes a certain light spring of unstretched length 33.0 cm. When one end is attached to the top of a door frame, and a 5.80-kg object is hung from the other end, the length of the spring is 42.50 cm. (a) Find its spring constant. (b) The load and the...
  19. O

    Fortran How to declare real constants in Fortran? Please help

    How do I declare constants beginning with "zero" in Fortran to get the output beginning with zero ? If I declare : I get the output: Thanks in advance
  20. V

    Determining the constants R and L of a coil

    We determined the constants R and L of a coil by placing it in series with a standard resistor of 10 ohms and reading the voltages on the terminals of Rs, the coil and the series circuit complete. What are the values of R and L for the following voltage readings at 60 Hz: Vrs = 20; Vcoil =...
  21. Z

    Dielectric Constant of Poly(allylamine hydrochloride)

    I am currently in a research lab working with various polymers. I have been searching for a while, with no luck, to locate the dielectric constant of PAH poly(allylamine hydrochloride). Can anyone provide me with this constant? Thanks.
  22. S

    Summing reactions/rate constants

    Hi! I have a couple of reactions whose rate constants are known: A + B -> C + D (reaction 1) C + B -> E + F (reaction 2) and I want to know the rate constants of the sum of these reactions. That is: A + 2B -> D + E + F (reaction 3) How may I know the rate constant for reaction 3...
  23. J

    Gravitational force and constants

    Homework Statement Three identical masses of 570 kg each are placed on the x axis. One mass is at x_1 = -10.0 cm, one is at the origin, and one is at x_2 = 43.0 cm. What is the magnitude of the net gravitational force F_grav on the mass at the origin due to the other two masses? Take the...
  24. J

    Calculating Time Constants for RC and RL Circuits | Simple Physics Homework Help

    Homework Statement Calculate the time constants of the following circuits I drew them in the attachment Homework Equations t=RC in a RC Circuit t= L/R in a RL Circuit The Attempt at a Solution Im not sure if in the first one, I would simply add the two...
  25. T

    Calculating elastic constants Cijkl

    Homework Statement Longnitudal and transverse soundwaves in nickel (FCC lattice) moves at velocities 5300m/s 3800m/s. Determine the elastic constants Cijkl Homework Equations v =\sqrt{C_{ij}/\rho} The Attempt at a Solution I guess I can calculate Cij with that equation...but I...
  26. M

    Static and dynamic spring constants

    Should the static spring constant and dynamic spring constant of the same spring be the same value (or very close to the same value)? I know the difference between the two is that static is found by measuring the displacement from equilibrium by adding different weights and dynamic is found by...
  27. E

    Finding Constants given certain constraints.

    1.Find a such that y=x2 - 2(x)1/2 + 1 is perpendicular to ay + 2x =2 when x=4 3.I have gotten as far as getting the slope of the normal line. I then rearranged the equation to y = (-2x+2)/ (a) and That is where I am stuck I am having a lot of trouble with these types of...
  28. A

    When working out the Uncertainties, what to do with the constants?

    Q=mcT, variables with uncertainties are m and T. If it were only Q=mT, the %uncertainty of Q would be %uncertainty of m + % uncertainty of T. But c=constant (no uncertainties), so what is the uncertainty of Q when Q=mcT? Do you just multiply the constant to the %uncertainties of m and T...
  29. R

    Equation for a circle in terms of constants A and B

    [Homework Statement If 0<a<b, find the radius R and center (h,k) of the circle that passes through the points (0,a) and (0,b) and is tangent to the x-axis at a point to the right of the origin. Homework Equations ((x-h)^2) + ((y-k)^2)=R^2 (equation of the circle centered around (h,k))...
  30. S

    Differential equations - finding constants

    Find values of the constants a and k so that y(x) = ax^k solves the differential equation; (dy/dx)^2 + [(3y^2)/(x^2)] + [(2y)/(x^4)] I tried substituiting ax^k into the DE but it did not work. I need to separate x and y but I cannot do it then I need to integrate it I think. I just...
  31. L

    Constants and multiverse possibilities

    Scientists have discovered that they are about 20 constants in nature that if they varied by more than 1% we would not exist. It's like the universe is finely tuned for life to exist. Now there's two possibilities, 1. the universe is intelligent, aware of itself,manages its evolution and plans...
  32. T

    How to calculate section constants for rectangular tubes?

    Hi. I was wondering how to calculate I and W for rectangular and quadratic tubes. I have formulas for massive rectangular and square sections and for circular tubes. I tried to make a formula for a square tube section, based on how the formula for the circular tube looks - but I didn't get...
  33. M

    Mathematica How can I vary physical constants in Mathematica plots?

    I have a function which depends on several physical constants, which I want to be able to vary each time I make a plot. What is the best way to do this?
  34. R

    Relation between torsional and linear spring constants for a cantilever beam?

    Hello, This should be a straight one for most of you. Given a cantilevered beam that has a force F applied across it (or at one end), causing a displacement d and deflection \theta , what is the relationship between the torsional spring constant k_{theta} and the linear spring constant k...
  35. M

    Understanding the Parabola's Constants: a, b, c

    Homework Statement The general equation for a parabola is y=ax²+bx+c, where a, b, c are constants. What are the units of each constant? Homework Equations y=ax²+bx+c The Attempt at a Solution The answer is a: 1/m; b: dimensionless; c: m How exactly did they get that answer in the book...
  36. E

    Applications of Equilibrium Constants

    Homework Statement At 1285*C the equilibrium constant for the reaction Br_2 (g) \Leftrightarrow 2Br (g). A 0.200L vessel containing an equilibrium mixture of the gasses has 0.245g of Br_2(g) in it. What is the mass of Br(g) in the vessel? Homework Equations None The Attempt at a...
  37. E

    Unitless constants and unitized forces

    Coupling constants are unitized or unitless. Forces are associated to unitized coupling constants like charge (e), gravity (G), etc. All unitless coupling constants that I know of, like the fine structure constant (\alpha), or the Lorentzian \beta, etc are ratios where the units cancel out...
  38. L

    Why are the electric and magnetic constants where they are?

    Epsilon0, the electric constant, and Mu0, the magnetic constant, were introduced in Coulomb's Constant and Ampere's Constant in order to make units and magnitudes match, in Coulomb's Law and Ampere's Force Law, respectively. But Coulomb's Constant is: 1/4 pi Epsilon0 and Ampere's Constant...
  39. apeiron

    Dimensionful vs dimensionless constants

    In describing physical reality, we have two classes of constants, the dimensionless and the dimensionful. http://en.wikipedia.org/wiki/Physical_constant Which is the more fundamental and why? And exactly what is the meaning of their difference? I have my own take of course. My feeling...
  40. M

    Ion exchange and stability constants

    Homework Statement In natural water containing 0.9 mmol/L calcium and 12 ug/L fulvic acid, determine the fraction of the fulvic acid that is bound to calcium (i.e. the ratio between the concentration of Ca-FA and total concentration of FA binding sites), assuming that calcium is the only metal...
  41. C

    Relating electric constants to the speed of light ?

    1/sqrt(EP)=c where E= Permittivity constant P= permeability constant . My teacher wanted us to think about this result that Maxwell got and how it would lead to problems and eventually lead to relativity can some one give me a hint what he is getting at this is not a home work...
  42. Z

    Differentiating y= Acosαx + Bsinαx and finding Constants

    Homework Statement Don't really know what to do with this one, any help welcome If A, B and α are constants, independent of x, and y= Acosαx + Bsinαx Evaluate the derivates y'=dy/dx y^n=d^2y/dx^2 Determine values of A, B and α such that y satisfies y^n+y=0 and y(0)=0, y'(0)=1...
  43. L

    Harmonic motion, finding analytic expressions for constants

    1. Find analytic expressions for the arbitrary constants A and phi in Equation 1 (found in Part A) in terms of the constants C and S in Equation 2 (found in Part B), which are now considered as given parameters. Express the amplitude A and phase phi (separated by a comma) in terms of C and S...
  44. Z

    Incompressiblitiy and unit length implies constants

    Let u,v\in C^1(R^2), and (u)^1+(v)^2=1,\partial_x u+ \partial_y v=0. Then u,v are constants. Is it right? How to prove?
  45. P

    Disoersion relation and lattice constants

    Dispersion relation and lattice constants I need to be able to calculate the period (which I believe is the lattice constant) for a 1D crystal given the energy wavevector relation. Is this possible? I also have to find the Bravais lattice of a 2D crystal give a similar relation. What is it...
  46. W

    Special invariants with few constants of motion

    Ordinarily, a system of N particles in d dimensions has 2Nd constants of motion, but there are certain invariants, like energy and angular momentum, that have a lot fewer. What's so special about these? Why do they have so few constants of motion?
  47. O

    Proving deltaT is Smaller for Larger Constants B & C

    Homework Statement The following equation is studied. This is the final equation i have come to after a lot of assumptions and simplifactions in a bubblepoint calculation. It refers to the difference between the previous T and the new T. I don't know how to continue with this problem...
  48. F

    Finding the Constants in a Motion Equation

    Homework Statement If s(0) = 0, v(1) = 24 and a(t) = 24t+6 find s(t) Homework Equations The Attempt at a Solution I know a(t) is s''(t) and v(t) is s'(t). however, How can I find s(t)?
  49. P

    Find constants s.t. the following expression holds for all n.

    Homework Statement Find constants c_1,c_2 (independent of n) such that the following holds for all n\in \mathbb{N}: \left| \sum^{2n}_{k=n+1} \frac{1}{k} - \log 2 - \frac{c_1}{n} \right| \le \frac{c_2}{n^2}. Homework Equations \log(2) = \sum^{\infty}_{k=1} (-1)^{k+1}\left( \frac{1}{k}...
  50. C

    Limit of an unknown constant expression

    Homework Statement find limit of x as it approaches infinite sqrt(x^2+ax)-sqrt(x^2+bx) a and b are not given Homework Equations The Attempt at a Solution Looking at this equation I first eliminated the square roots. After simplifying i ended up with ax-bx/sqrt(x^2+ax)+sqrt(x^2+bx)...
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